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 $217.78   3.153%   $224.6466   $224.65   $224.65   $224.60  
  Purchase #2 $89.80   9.394%   $98.2358   $98.24   $98.25   $98.20  
  Purchase #3 $162.43   8.599%   $176.3974   $176.40   $176.40   $176.40  
  Purchase #4 $29.93   8.228%   $32.3926   $32.39   $32.40   $32.40  
  Purchase #5 $107.90   9.753%   $118.4235   $118.42   $118.40   $118.40  
  Purchase #6 $148.45   8.857%   $161.5982   $161.60   $161.60   $161.60  
  Purchase #7 $215.32   7.837%   $232.1946   $232.19   $232.20   $232.20  
  7 purchase totals = $971.61       $1,043.8887   $1,043.89   $1,043.90   $1,043.80