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 $161.79   3.822%   $167.9736   $167.97   $167.95   $168.00  
  Purchase #2 $125.45   5.395%   $132.218   $132.22   $132.20   $132.20  
  Purchase #3 $106.36   4.197%   $110.8239   $110.82   $110.80   $110.80  
  Purchase #4 $104.31   4.494%   $108.9977   $109.00   $109.00   $109.00  
  Purchase #5 $58.46   8.377%   $63.3572   $63.36   $63.35   $63.40  
  Purchase #6 $112.34   4.145%   $116.9965   $117.00   $117.00   $117.00  
  Purchase #7 $134.39   4.113%   $139.9175   $139.92   $139.90   $139.90  
  7 purchase totals = $803.10       $840.2844   $840.29   $840.20   $840.30