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 $88.68   4.377%   $92.5615   $92.56   $92.55   $92.60  
  Purchase #2 $222.42   9.413%   $243.3564   $243.36   $243.35   $243.40  
  Purchase #3 $113.44   10.516%   $125.3694   $125.37   $125.35   $125.40  
  Purchase #4 $106.83   12.211%   $119.875   $119.88   $119.90   $119.90  
  Purchase #5 $181.77   11.823%   $203.2607   $203.26   $203.25   $203.30  
  Purchase #6 $34.52   11.745%   $38.5744   $38.57   $38.55   $38.60  
  Purchase #7 $17.45   4.848%   $18.296   $18.30   $18.30   $18.30  
  7 purchase totals = $765.11       $841.2934   $841.30   $841.25   $841.50