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 $80.90   13.731%   $92.0084   $92.01   $92.00   $92.00  
  Purchase #2 $236.71   12.343%   $265.9271   $265.93   $265.95   $265.90  
  Purchase #3 $51.36   4.705%   $53.7765   $53.78   $53.80   $53.80  
  Purchase #4 $117.46   12.596%   $132.2553   $132.26   $132.25   $132.30  
  Purchase #5 $189.44   8.767%   $206.0482   $206.05   $206.05   $206.00  
  Purchase #6 $127.52   13.147%   $144.2851   $144.29   $144.30   $144.30  
  Purchase #7 $185.40   11.872%   $207.4107   $207.41   $207.40   $207.40  
  7 purchase totals = $988.79       $1,101.7113   $1,101.73   $1,101.75   $1,101.70