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 $221.83   13.268%   $251.2624   $251.26   $251.25   $251.30  
  Purchase #2 $28.78   6.658%   $30.6962   $30.70   $30.70   $30.70  
  Purchase #3 $68.71   3.837%   $71.3464   $71.35   $71.35   $71.30  
  Purchase #4 $238.81   3.426%   $246.9916   $246.99   $247.00   $247.00  
  Purchase #5 $101.38   11.355%   $112.8917   $112.89   $112.90   $112.90  
  Purchase #6 $22.50   13.391%   $25.513   $25.51   $25.50   $25.50  
  Purchase #7 $41.77   6.407%   $44.4462   $44.45   $44.45   $44.40  
  7 purchase totals = $723.78       $783.1475   $783.15   $783.15   $783.10