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 $66.46   13.674%   $75.5477   $75.55   $75.55   $75.50  
  Purchase #2 $42.47   11.793%   $47.4785   $47.48   $47.50   $47.50  
  Purchase #3 $204.36   4.572%   $213.7033   $213.70   $213.70   $213.70  
  Purchase #4 $82.56   12.443%   $92.8329   $92.83   $92.85   $92.80  
  Purchase #5 $39.68   4.709%   $41.5485   $41.55   $41.55   $41.50  
  Purchase #6 $205.36   9.580%   $225.0335   $225.03   $225.05   $225.00  
  Purchase #7 $220.78   13.291%   $250.1239   $250.12   $250.10   $250.10  
  7 purchase totals = $861.67       $946.2683   $946.26   $946.30   $946.10