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 $69.65   5.193%   $73.2669   $73.27   $73.25   $73.30  
  Purchase #2 $197.54   3.473%   $204.4006   $204.40   $204.40   $204.40  
  Purchase #3 $136.92   12.506%   $154.0432   $154.04   $154.05   $154.00  
  Purchase #4 $200.88   4.257%   $209.4315   $209.43   $209.45   $209.40  
  Purchase #5 $119.60   5.215%   $125.8371   $125.84   $125.85   $125.80  
  Purchase #6 $6.38   8.161%   $6.9007   $6.90   $6.90   $6.90  
  Purchase #7 $93.29   4.144%   $97.1559   $97.16   $97.15   $97.20  
  7 purchase totals = $824.26       $871.0359   $871.04   $871.05   $871.00