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 $58.92   6.370%   $62.6732   $62.67   $62.65   $62.70  
  Purchase #2 $102.28   13.287%   $115.8699   $115.87   $115.85   $115.90  
  Purchase #3 $100.47   12.559%   $113.088   $113.09   $113.10   $113.10  
  Purchase #4 $207.57   4.517%   $216.9459   $216.95   $216.95   $216.90  
  Purchase #5 $36.57   6.317%   $38.8801   $38.88   $38.90   $38.90  
  Purchase #6 $198.35   5.701%   $209.6579   $209.66   $209.65   $209.70  
  Purchase #7 $189.85   11.255%   $211.2176   $211.22   $211.20   $211.20  
  7 purchase totals = $894.01       $968.3326   $968.34   $968.30   $968.40