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 $187.90   7.853%   $202.6558   $202.66   $202.65   $202.70  
  Purchase #2 $127.95   4.113%   $133.2126   $133.21   $133.20   $133.20  
  Purchase #3 $93.91   8.657%   $102.0398   $102.04   $102.05   $102.00  
  Purchase #4 $73.44   5.182%   $77.2457   $77.25   $77.25   $77.20  
  Purchase #5 $122.82   3.313%   $126.889   $126.89   $126.90   $126.90  
  Purchase #6 $131.25   6.163%   $139.3389   $139.34   $139.35   $139.30  
  Purchase #7 $224.57   7.762%   $242.0011   $242.00   $242.00   $242.00  
  7 purchase totals = $961.84       $1,023.3829   $1,023.39   $1,023.40   $1,023.30