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 $212.88   13.480%   $241.5762   $241.58   $241.60   $241.60  
  Purchase #2 $51.93   12.452%   $58.3963   $58.40   $58.40   $58.40  
  Purchase #3 $85.31   11.313%   $94.9611   $94.96   $94.95   $95.00  
  Purchase #4 $194.39   5.549%   $205.1767   $205.18   $205.20   $205.20  
  Purchase #5 $143.76   7.680%   $154.8008   $154.80   $154.80   $154.80  
  Purchase #6 $158.41   9.829%   $173.9801   $173.98   $174.00   $174.00  
  Purchase #7 $54.36   3.663%   $56.3512   $56.35   $56.35   $56.40  
  7 purchase totals = $901.04       $985.2424   $985.25   $985.30   $985.40