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 $178.58   8.713%   $194.1397   $194.14   $194.15   $194.10  
  Purchase #2 $30.79   5.183%   $32.3858   $32.39   $32.40   $32.40  
  Purchase #3 $239.51   8.561%   $260.0145   $260.01   $260.00   $260.00  
  Purchase #4 $215.36   9.301%   $235.3906   $235.39   $235.40   $235.40  
  Purchase #5 $227.30   4.282%   $237.033   $237.03   $237.05   $237.00  
  Purchase #6 $180.76   8.214%   $195.6076   $195.61   $195.60   $195.60  
  Purchase #7 $135.44   12.629%   $152.5447   $152.54   $152.55   $152.50  
  7 purchase totals = $1,207.74       $1,307.1159   $1,307.11   $1,307.15   $1,307.00