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 $226.78   8.805%   $246.748   $246.75   $246.75   $246.70  
  Purchase #2 $60.97   5.129%   $64.0972   $64.10   $64.10   $64.10  
  Purchase #3 $25.61   12.444%   $28.7969   $28.80   $28.80   $28.80  
  Purchase #4 $174.76   7.702%   $188.22   $188.22   $188.20   $188.20  
  Purchase #5 $204.62   6.321%   $217.554   $217.55   $217.55   $217.60  
  Purchase #6 $14.87   13.154%   $16.826   $16.83   $16.85   $16.80  
  Purchase #7 $59.35   8.743%   $64.539   $64.54   $64.55   $64.50  
  7 purchase totals = $766.96       $826.7811   $826.79   $826.80   $826.70