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 $47.69   4.270%   $49.7264   $49.73   $49.75   $49.70  
  Purchase #2 $120.95   8.556%   $131.2985   $131.30   $131.30   $131.30  
  Purchase #3 $172.99   8.829%   $188.2633   $188.26   $188.25   $188.30  
  Purchase #4 $182.94   8.389%   $198.2868   $198.29   $198.30   $198.30  
  Purchase #5 $23.52   4.632%   $24.6094   $24.61   $24.60   $24.60  
  Purchase #6 $204.48   8.477%   $221.8138   $221.81   $221.80   $221.80  
  Purchase #7 $18.34   9.266%   $20.0394   $20.04   $20.05   $20.00  
  7 purchase totals = $770.91       $834.0376   $834.04   $834.05   $834.00