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 $161.68   4.620%   $169.1496   $169.15   $169.15   $169.10  
  Purchase #2 $164.33   12.494%   $184.8614   $184.86   $184.85   $184.90  
  Purchase #3 $185.77   8.470%   $201.5047   $201.50   $201.50   $201.50  
  Purchase #4 $89.41   6.859%   $95.5426   $95.54   $95.55   $95.50  
  Purchase #5 $211.94   8.869%   $230.737   $230.74   $230.75   $230.70  
  Purchase #6 $215.52   7.835%   $232.406   $232.41   $232.40   $232.40  
  Purchase #7 $151.89   6.360%   $161.5502   $161.55   $161.55   $161.60  
  7 purchase totals = $1,180.54       $1,275.7515   $1,275.75   $1,275.75   $1,275.70