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 $68.97   4.786%   $72.2709   $72.27   $72.25   $72.30  
  Purchase #2 $205.33   11.164%   $228.253   $228.25   $228.25   $228.30  
  Purchase #3 $125.94   11.397%   $140.2934   $140.29   $140.30   $140.30  
  Purchase #4 $23.49   3.236%   $24.2501   $24.25   $24.25   $24.30  
  Purchase #5 $137.65   8.328%   $149.1135   $149.11   $149.10   $149.10  
  Purchase #6 $124.64   5.231%   $131.1599   $131.16   $131.15   $131.20  
  Purchase #7 $161.29   13.449%   $182.9819   $182.98   $183.00   $183.00  
  7 purchase totals = $847.31       $928.3227   $928.31   $928.30   $928.50