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 $70.93   7.411%   $76.1866   $76.19   $76.20   $76.20  
  Purchase #2 $176.97   5.826%   $187.2803   $187.28   $187.30   $187.30  
  Purchase #3 $24.82   6.175%   $26.3526   $26.35   $26.35   $26.40  
  Purchase #4 $247.72   4.600%   $259.1151   $259.12   $259.10   $259.10  
  Purchase #5 $46.77   11.199%   $52.0078   $52.01   $52.00   $52.00  
  Purchase #6 $139.29   13.530%   $158.1359   $158.14   $158.15   $158.10  
  Purchase #7 $191.83   5.528%   $202.4344   $202.43   $202.45   $202.40  
  7 purchase totals = $898.33       $961.5127   $961.52   $961.55   $961.50