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 $54.63   12.609%   $61.5183   $61.52   $61.50   $61.50  
  Purchase #2 $71.59   10.696%   $79.2473   $79.25   $79.25   $79.20  
  Purchase #3 $124.45   11.541%   $138.8128   $138.81   $138.80   $138.80  
  Purchase #4 $193.62   11.151%   $215.2106   $215.21   $215.20   $215.20  
  Purchase #5 $57.31   12.575%   $64.5167   $64.52   $64.50   $64.50  
  Purchase #6 $216.32   11.400%   $240.9805   $240.98   $241.00   $241.00  
  Purchase #7 $115.89   8.423%   $125.6514   $125.65   $125.65   $125.70  
  7 purchase totals = $833.81       $925.9376   $925.94   $925.90   $925.90