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 $219.53   12.282%   $246.4927   $246.49   $246.50   $246.50  
  Purchase #2 $114.94   9.351%   $125.688   $125.69   $125.70   $125.70  
  Purchase #3 $44.87   4.655%   $46.9587   $46.96   $46.95   $47.00  
  Purchase #4 $22.93   11.124%   $25.4807   $25.48   $25.50   $25.50  
  Purchase #5 $168.61   13.717%   $191.7382   $191.74   $191.75   $191.70  
  Purchase #6 $144.40   4.806%   $151.3399   $151.34   $151.35   $151.30  
  Purchase #7 $100.33   6.446%   $106.7973   $106.80   $106.80   $106.80  
  7 purchase totals = $815.61       $894.4955   $894.50   $894.55   $894.50