Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $116.52   13.152%   $131.8447   $131.84   $131.85   $131.80  
  Purchase #2 $179.84   12.105%   $201.6096   $201.61   $201.60   $201.60  
  Purchase #3 $165.27   9.190%   $180.4583   $180.46   $180.45   $180.50  
  Purchase #4 $232.58   10.644%   $257.3358   $257.34   $257.35   $257.30  
  Purchase #5 $151.33   8.855%   $164.7303   $164.73   $164.75   $164.70  
  Purchase #6 $219.66   10.515%   $242.7572   $242.76   $242.75   $242.80  
  Purchase #7 $121.74   4.784%   $127.564   $127.56   $127.55   $127.60  
  7 purchase totals = $1,186.94       $1,306.2999   $1,306.30   $1,306.30   $1,306.30