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 $48.83   13.201%   $55.276   $55.28   $55.30   $55.30  
  Purchase #2 $111.78   6.810%   $119.3922   $119.39   $119.40   $119.40  
  Purchase #3 $205.93   8.520%   $223.4752   $223.48   $223.50   $223.50  
  Purchase #4 $101.41   7.184%   $108.6953   $108.70   $108.70   $108.70  
  Purchase #5 $212.95   12.768%   $240.1395   $240.14   $240.15   $240.10  
  Purchase #6 $151.42   6.827%   $161.7574   $161.76   $161.75   $161.80  
  Purchase #7 $230.38   13.718%   $261.9835   $261.98   $262.00   $262.00  
  7 purchase totals = $1,062.70       $1,170.7191   $1,170.73   $1,170.80   $1,170.80