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 $109.71   8.477%   $119.0101   $119.01   $119.00   $119.00  
  Purchase #2 $228.44   9.347%   $249.7923   $249.79   $249.80   $249.80  
  Purchase #3 $112.33   4.202%   $117.0501   $117.05   $117.05   $117.10  
  Purchase #4 $109.95   9.529%   $120.4271   $120.43   $120.45   $120.40  
  Purchase #5 $250.53   3.788%   $260.0201   $260.02   $260.00   $260.00  
  Purchase #6 $56.44   11.587%   $62.9797   $62.98   $63.00   $63.00  
  Purchase #7 $166.45   6.612%   $177.4557   $177.46   $177.45   $177.50  
  7 purchase totals = $1,033.85       $1,106.7351   $1,106.74   $1,106.75   $1,106.80