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 $232.49   13.592%   $264.09   $264.09   $264.10   $264.10  
  Purchase #2 $187.95   6.272%   $199.7382   $199.74   $199.75   $199.70  
  Purchase #3 $12.95   10.233%   $14.2752   $14.28   $14.30   $14.30  
  Purchase #4 $148.84   5.772%   $157.431   $157.43   $157.45   $157.40  
  Purchase #5 $113.90   3.850%   $118.2852   $118.29   $118.30   $118.30  
  Purchase #6 $28.87   8.548%   $31.3378   $31.34   $31.35   $31.30  
  Purchase #7 $95.80   3.851%   $99.4893   $99.49   $99.50   $99.50  
  7 purchase totals = $820.80       $884.6467   $884.66   $884.75   $884.60