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 $117.45   8.111%   $126.9764   $126.98   $127.00   $127.00  
  Purchase #2 $128.55   5.753%   $135.9455   $135.95   $135.95   $135.90  
  Purchase #3 $69.32   11.395%   $77.219   $77.22   $77.20   $77.20  
  Purchase #4 $247.88   6.634%   $264.3244   $264.32   $264.30   $264.30  
  Purchase #5 $15.29   4.115%   $15.9192   $15.92   $15.90   $15.90  
  Purchase #6 $12.79   6.631%   $13.6381   $13.64   $13.65   $13.60  
  Purchase #7 $61.34   7.663%   $66.0405   $66.04   $66.05   $66.00  
  7 purchase totals = $652.62       $700.0631   $700.07   $700.05   $699.90