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 $247.46   9.613%   $271.2483   $271.25   $271.25   $271.20  
  Purchase #2 $181.98   12.515%   $204.7548   $204.75   $204.75   $204.80  
  Purchase #3 $85.30   8.186%   $92.2827   $92.28   $92.30   $92.30  
  Purchase #4 $214.25   4.661%   $224.2362   $224.24   $224.25   $224.20  
  Purchase #5 $183.26   4.477%   $191.4646   $191.46   $191.45   $191.50  
  Purchase #6 $59.82   11.861%   $66.9153   $66.92   $66.90   $66.90  
  Purchase #7 $67.36   5.797%   $71.2649   $71.26   $71.25   $71.30  
  7 purchase totals = $1,039.43       $1,122.1668   $1,122.16   $1,122.15   $1,122.20