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 $193.71   5.319%   $204.0134   $204.01   $204.00   $204.00  
  Purchase #2 $204.96   10.756%   $227.0055   $227.01   $227.00   $227.00  
  Purchase #3 $83.73   12.106%   $93.8664   $93.87   $93.85   $93.90  
  Purchase #4 $61.91   8.444%   $67.1377   $67.14   $67.15   $67.10  
  Purchase #5 $93.57   13.645%   $106.3376   $106.34   $106.35   $106.30  
  Purchase #6 $203.61   5.616%   $215.0447   $215.04   $215.05   $215.00  
  Purchase #7 $112.99   4.802%   $118.4158   $118.42   $118.40   $118.40  
  7 purchase totals = $954.48       $1,031.8211   $1,031.83   $1,031.80   $1,031.70