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 $54.37   6.617%   $57.9677   $57.97   $57.95   $58.00  
  Purchase #2 $104.95   7.622%   $112.9493   $112.95   $112.95   $112.90  
  Purchase #3 $124.92   10.195%   $137.6556   $137.66   $137.65   $137.70  
  Purchase #4 $90.43   11.659%   $100.9732   $100.97   $100.95   $101.00  
  Purchase #5 $192.99   5.319%   $203.2551   $203.26   $203.25   $203.30  
  Purchase #6 $122.61   3.758%   $127.2177   $127.22   $127.20   $127.20  
  Purchase #7 $195.61   3.736%   $202.918   $202.92   $202.90   $202.90  
  7 purchase totals = $885.88       $942.9366   $942.95   $942.85   $943.00