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 $24.57   5.477%   $25.9157   $25.92   $25.90   $25.90  
  Purchase #2 $82.78   3.296%   $85.5084   $85.51   $85.50   $85.50  
  Purchase #3 $219.90   4.407%   $229.591   $229.59   $229.60   $229.60  
  Purchase #4 $218.94   3.432%   $226.454   $226.45   $226.45   $226.50  
  Purchase #5 $77.44   13.443%   $87.8503   $87.85   $87.85   $87.90  
  Purchase #6 $82.47   11.584%   $92.0233   $92.02   $92.00   $92.00  
  Purchase #7 $187.96   10.637%   $207.9533   $207.95   $207.95   $208.00  
  7 purchase totals = $894.06       $955.2960   $955.29   $955.25   $955.40