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 $107.25   11.351%   $119.4239   $119.42   $119.40   $119.40  
  Purchase #2 $172.86   8.146%   $186.9412   $186.94   $186.95   $186.90  
  Purchase #3 $197.56   7.431%   $212.2407   $212.24   $212.25   $212.20  
  Purchase #4 $56.89   11.266%   $63.2992   $63.30   $63.30   $63.30  
  Purchase #5 $212.31   11.283%   $236.2649   $236.26   $236.25   $236.30  
  Purchase #6 $161.26   9.345%   $176.3297   $176.33   $176.35   $176.30  
  Purchase #7 $47.32   3.364%   $48.9118   $48.91   $48.90   $48.90  
  7 purchase totals = $955.45       $1,043.4114   $1,043.40   $1,043.40   $1,043.30