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 $173.25   6.627%   $184.7313   $184.73   $184.75   $184.70  
  Purchase #2 $82.97   13.841%   $94.4539   $94.45   $94.45   $94.50  
  Purchase #3 $125.53   3.675%   $130.1432   $130.14   $130.15   $130.10  
  Purchase #4 $24.76   4.605%   $25.9002   $25.90   $25.90   $25.90  
  Purchase #5 $118.50   5.867%   $125.4524   $125.45   $125.45   $125.50  
  Purchase #6 $86.30   8.145%   $93.3291   $93.33   $93.35   $93.30  
  Purchase #7 $55.67   10.154%   $61.3227   $61.32   $61.30   $61.30  
  7 purchase totals = $666.98       $715.3328   $715.32   $715.35   $715.30