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 $58.89   4.810%   $61.7226   $61.72   $61.70   $61.70  
  Purchase #2 $158.83   10.822%   $176.0186   $176.02   $176.00   $176.00  
  Purchase #3 $238.96   13.436%   $271.0667   $271.07   $271.05   $271.10  
  Purchase #4 $19.39   9.723%   $21.2753   $21.28   $21.30   $21.30  
  Purchase #5 $203.74   13.556%   $231.359   $231.36   $231.35   $231.40  
  Purchase #6 $33.61   8.682%   $36.528   $36.53   $36.55   $36.50  
  Purchase #7 $141.68   13.668%   $161.0448   $161.04   $161.05   $161.00  
  7 purchase totals = $855.10       $959.0150   $959.02   $959.00   $959.00