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 $24.35   5.655%   $25.727   $25.73   $25.75   $25.70  
  Purchase #2 $68.97   9.834%   $75.7525   $75.75   $75.75   $75.80  
  Purchase #3 $14.43   3.370%   $14.9163   $14.92   $14.90   $14.90  
  Purchase #4 $249.95   13.516%   $283.7332   $283.73   $283.75   $283.70  
  Purchase #5 $30.67   3.102%   $31.6214   $31.62   $31.60   $31.60  
  Purchase #6 $110.25   3.590%   $114.208   $114.21   $114.20   $114.20  
  Purchase #7 $219.50   13.218%   $248.5135   $248.51   $248.50   $248.50  
  7 purchase totals = $718.12       $794.4719   $794.47   $794.45   $794.40