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 $176.80   3.483%   $182.9579   $182.96   $182.95   $183.00  
  Purchase #2 $51.95   12.124%   $58.2484   $58.25   $58.25   $58.20  
  Purchase #3 $208.39   7.765%   $224.5715   $224.57   $224.55   $224.60  
  Purchase #4 $162.52   9.639%   $178.1853   $178.19   $178.20   $178.20  
  Purchase #5 $72.98   13.536%   $82.8586   $82.86   $82.85   $82.90  
  Purchase #6 $10.46   8.360%   $11.3345   $11.33   $11.35   $11.30  
  Purchase #7 $21.60   9.664%   $23.6874   $23.69   $23.70   $23.70  
  7 purchase totals = $704.70       $761.8436   $761.85   $761.85   $761.90