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 $44.95   12.650%   $50.6362   $50.64   $50.65   $50.60  
  Purchase #2 $67.29   12.392%   $75.6286   $75.63   $75.65   $75.60  
  Purchase #3 $195.35   12.361%   $219.4972   $219.50   $219.50   $219.50  
  Purchase #4 $88.64   11.545%   $98.8735   $98.87   $98.85   $98.90  
  Purchase #5 $130.64   12.827%   $147.3972   $147.40   $147.40   $147.40  
  Purchase #6 $201.62   13.741%   $229.3246   $229.32   $229.30   $229.30  
  Purchase #7 $185.38   8.492%   $201.1225   $201.12   $201.10   $201.10  
  7 purchase totals = $913.87       $1,022.4798   $1,022.48   $1,022.45   $1,022.40