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 $66.51   11.482%   $74.1467   $74.15   $74.15   $74.10  
  Purchase #2 $215.34   9.855%   $236.5618   $236.56   $236.55   $236.60  
  Purchase #3 $138.74   10.107%   $152.7625   $152.76   $152.75   $152.80  
  Purchase #4 $14.42   10.453%   $15.9273   $15.93   $15.95   $15.90  
  Purchase #5 $58.80   9.374%   $64.3119   $64.31   $64.30   $64.30  
  Purchase #6 $174.88   10.131%   $192.5971   $192.60   $192.60   $192.60  
  Purchase #7 $171.77   9.603%   $188.2651   $188.27   $188.25   $188.30  
  7 purchase totals = $840.46       $924.5724   $924.58   $924.55   $924.60