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 $111.85   4.824%   $117.2456   $117.25   $117.25   $117.20  
  Purchase #2 $63.98   5.256%   $67.3428   $67.34   $67.35   $67.30  
  Purchase #3 $226.77   9.845%   $249.0955   $249.10   $249.10   $249.10  
  Purchase #4 $89.90   10.583%   $99.4141   $99.41   $99.40   $99.40  
  Purchase #5 $80.40   5.723%   $85.0013   $85.00   $85.00   $85.00  
  Purchase #6 $31.98   3.160%   $32.9906   $32.99   $33.00   $33.00  
  Purchase #7 $229.54   6.255%   $243.8977   $243.90   $243.90   $243.90  
  7 purchase totals = $834.42       $894.9876   $894.99   $895.00   $894.90