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 $62.43   9.786%   $68.5394   $68.54   $68.55   $68.50  
  Purchase #2 $67.62   11.183%   $75.1819   $75.18   $75.20   $75.20  
  Purchase #3 $90.70   11.795%   $101.3981   $101.40   $101.40   $101.40  
  Purchase #4 $97.38   11.823%   $108.8932   $108.89   $108.90   $108.90  
  Purchase #5 $227.83   12.574%   $256.4773   $256.48   $256.50   $256.50  
  Purchase #6 $34.90   9.760%   $38.3062   $38.31   $38.30   $38.30  
  Purchase #7 $53.74   9.717%   $58.9619   $58.96   $58.95   $59.00  
  7 purchase totals = $634.60       $707.7580   $707.76   $707.80   $707.80