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 $75.37   12.197%   $84.5629   $84.56   $84.55   $84.60  
  Purchase #2 $126.67   11.782%   $141.5943   $141.59   $141.60   $141.60  
  Purchase #3 $116.90   7.123%   $125.2268   $125.23   $125.25   $125.20  
  Purchase #4 $81.36   12.493%   $91.5243   $91.52   $91.50   $91.50  
  Purchase #5 $178.76   8.604%   $194.1405   $194.14   $194.15   $194.10  
  Purchase #6 $31.73   13.507%   $36.0158   $36.02   $36.00   $36.00  
  Purchase #7 $108.82   5.461%   $114.7627   $114.76   $114.75   $114.80  
  7 purchase totals = $719.61       $787.8273   $787.82   $787.80   $787.80