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 $67.27   6.530%   $71.6627   $71.66   $71.65   $71.70  
  Purchase #2 $31.45   7.173%   $33.7059   $33.71   $33.70   $33.70  
  Purchase #3 $146.97   11.620%   $164.0479   $164.05   $164.05   $164.00  
  Purchase #4 $188.65   13.410%   $213.948   $213.95   $213.95   $213.90  
  Purchase #5 $139.80   7.662%   $150.5115   $150.51   $150.50   $150.50  
  Purchase #6 $33.80   13.411%   $38.3329   $38.33   $38.35   $38.30  
  Purchase #7 $237.40   7.414%   $255.0008   $255.00   $255.00   $255.00  
  7 purchase totals = $845.34       $927.2097   $927.21   $927.20   $927.10