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 $68.58   8.816%   $74.626   $74.63   $74.65   $74.60  
  Purchase #2 $73.46   4.746%   $76.9464   $76.95   $76.95   $76.90  
  Purchase #3 $202.92   6.495%   $216.0997   $216.10   $216.10   $216.10  
  Purchase #4 $129.78   5.554%   $136.988   $136.99   $137.00   $137.00  
  Purchase #5 $105.37   13.412%   $119.5022   $119.50   $119.50   $119.50  
  Purchase #6 $171.54   9.658%   $188.1073   $188.11   $188.10   $188.10  
  Purchase #7 $88.56   12.428%   $99.5662   $99.57   $99.55   $99.60  
  7 purchase totals = $840.21       $911.8358   $911.85   $911.85   $911.80