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 $101.83   11.826%   $113.8724   $113.87   $113.85   $113.90  
  Purchase #2 $167.56   6.195%   $177.9403   $177.94   $177.95   $177.90  
  Purchase #3 $249.44   6.857%   $266.5441   $266.54   $266.55   $266.50  
  Purchase #4 $126.53   11.719%   $141.3581   $141.36   $141.35   $141.40  
  Purchase #5 $215.52   9.505%   $236.0052   $236.01   $236.00   $236.00  
  Purchase #6 $97.88   4.663%   $102.4441   $102.44   $102.45   $102.40  
  Purchase #7 $234.72   13.303%   $265.9448   $265.94   $265.95   $265.90  
  7 purchase totals = $1,193.48       $1,304.1090   $1,304.10   $1,304.10   $1,304.00