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 $47.67   7.105%   $51.057   $51.06   $51.05   $51.10  
  Purchase #2 $212.92   6.323%   $226.3829   $226.38   $226.40   $226.40  
  Purchase #3 $35.45   7.212%   $38.0067   $38.01   $38.00   $38.00  
  Purchase #4 $126.76   3.648%   $131.3842   $131.38   $131.40   $131.40  
  Purchase #5 $81.50   7.227%   $87.39   $87.39   $87.40   $87.40  
  Purchase #6 $89.27   4.377%   $93.1773   $93.18   $93.20   $93.20  
  Purchase #7 $210.85   4.489%   $220.3151   $220.32   $220.30   $220.30  
  7 purchase totals = $804.42       $847.7132   $847.72   $847.75   $847.80