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 $95.28   3.220%   $98.348   $98.35   $98.35   $98.30  
  Purchase #2 $11.68   13.732%   $13.2839   $13.28   $13.30   $13.30  
  Purchase #3 $196.81   12.743%   $221.8895   $221.89   $221.90   $221.90  
  Purchase #4 $244.73   4.315%   $255.2901   $255.29   $255.30   $255.30  
  Purchase #5 $25.91   12.347%   $29.1091   $29.11   $29.10   $29.10  
  Purchase #6 $208.96   8.719%   $227.1792   $227.18   $227.20   $227.20  
  Purchase #7 $11.35   8.701%   $12.3376   $12.34   $12.35   $12.30  
  7 purchase totals = $794.72       $857.4374   $857.44   $857.50   $857.40