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 $180.93   9.294%   $197.7456   $197.75   $197.75   $197.70  
  Purchase #2 $242.91   11.589%   $271.0608   $271.06   $271.05   $271.10  
  Purchase #3 $63.94   13.204%   $72.3826   $72.38   $72.40   $72.40  
  Purchase #4 $66.29   3.191%   $68.4053   $68.41   $68.40   $68.40  
  Purchase #5 $83.99   13.587%   $95.4017   $95.40   $95.40   $95.40  
  Purchase #6 $192.86   11.685%   $215.3957   $215.40   $215.40   $215.40  
  Purchase #7 $210.54   11.231%   $234.1857   $234.19   $234.20   $234.20  
  7 purchase totals = $1,041.46       $1,154.5774   $1,154.59   $1,154.60   $1,154.60