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 $43.46   8.673%   $47.2293   $47.23   $47.25   $47.20  
  Purchase #2 $229.59   9.127%   $250.5447   $250.54   $250.55   $250.50  
  Purchase #3 $141.93   9.360%   $155.2146   $155.21   $155.20   $155.20  
  Purchase #4 $95.61   9.606%   $104.7943   $104.79   $104.80   $104.80  
  Purchase #5 $68.79   7.741%   $74.115   $74.12   $74.10   $74.10  
  Purchase #6 $67.73   11.387%   $75.4424   $75.44   $75.45   $75.40  
  Purchase #7 $110.85   3.325%   $114.5358   $114.54   $114.55   $114.50  
  7 purchase totals = $757.96       $821.8761   $821.87   $821.90   $821.70