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 $106.86   12.248%   $119.9482   $119.95   $119.95   $119.90  
  Purchase #2 $246.55   5.834%   $260.9337   $260.93   $260.95   $260.90  
  Purchase #3 $155.35   3.768%   $161.2036   $161.20   $161.20   $161.20  
  Purchase #4 $169.81   9.113%   $185.2848   $185.28   $185.30   $185.30  
  Purchase #5 $7.61   12.695%   $8.5761   $8.58   $8.60   $8.60  
  Purchase #6 $249.87   11.819%   $279.4021   $279.40   $279.40   $279.40  
  Purchase #7 $158.44   4.378%   $165.3765   $165.38   $165.40   $165.40  
  7 purchase totals = $1,094.49       $1,180.7250   $1,180.72   $1,180.80   $1,180.70