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 $73.87   3.519%   $76.4695   $76.47   $76.45   $76.50  
  Purchase #2 $191.72   7.771%   $206.6186   $206.62   $206.60   $206.60  
  Purchase #3 $58.68   6.642%   $62.5775   $62.58   $62.60   $62.60  
  Purchase #4 $176.58   11.676%   $197.1975   $197.20   $197.20   $197.20  
  Purchase #5 $165.65   7.398%   $177.9048   $177.90   $177.90   $177.90  
  Purchase #6 $6.47   9.594%   $7.0907   $7.09   $7.10   $7.10  
  Purchase #7 $193.58   6.570%   $206.2982   $206.30   $206.30   $206.30  
  7 purchase totals = $866.55       $934.1568   $934.16   $934.15   $934.20