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 $177.27   11.484%   $197.6277   $197.63   $197.65   $197.60  
  Purchase #2 $111.56   12.399%   $125.3923   $125.39   $125.40   $125.40  
  Purchase #3 $236.38   4.838%   $247.8161   $247.82   $247.80   $247.80  
  Purchase #4 $32.43   6.697%   $34.6018   $34.60   $34.60   $34.60  
  Purchase #5 $188.85   11.406%   $210.3902   $210.39   $210.40   $210.40  
  Purchase #6 $181.64   11.661%   $202.821   $202.82   $202.80   $202.80  
  Purchase #7 $227.44   3.247%   $234.825   $234.83   $234.85   $234.80  
  7 purchase totals = $1,155.57       $1,253.4741   $1,253.48   $1,253.50   $1,253.40