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 $68.66   11.377%   $76.4714   $76.47   $76.45   $76.50  
  Purchase #2 $170.94   10.460%   $188.8203   $188.82   $188.80   $188.80  
  Purchase #3 $147.96   8.107%   $159.9551   $159.96   $159.95   $160.00  
  Purchase #4 $10.29   12.220%   $11.5474   $11.55   $11.55   $11.50  
  Purchase #5 $84.58   4.734%   $88.584   $88.58   $88.60   $88.60  
  Purchase #6 $98.63   10.650%   $109.1341   $109.13   $109.15   $109.10  
  Purchase #7 $244.87   10.520%   $270.6303   $270.63   $270.65   $270.60  
  7 purchase totals = $825.93       $905.1426   $905.14   $905.15   $905.10