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 $106.46   11.745%   $118.9637   $118.96   $118.95   $119.00  
  Purchase #2 $18.67   5.665%   $19.7277   $19.73   $19.75   $19.70  
  Purchase #3 $131.37   11.317%   $146.2371   $146.24   $146.25   $146.20  
  Purchase #4 $114.76   5.813%   $121.431   $121.43   $121.45   $121.40  
  Purchase #5 $61.98   12.717%   $69.862   $69.86   $69.85   $69.90  
  Purchase #6 $149.43   4.425%   $156.0423   $156.04   $156.05   $156.00  
  Purchase #7 $187.83   9.581%   $205.826   $205.83   $205.85   $205.80  
  7 purchase totals = $770.50       $838.0898   $838.09   $838.15   $838.00