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 $54.26   9.798%   $59.5764   $59.58   $59.60   $59.60  
  Purchase #2 $107.95   5.567%   $113.9596   $113.96   $113.95   $114.00  
  Purchase #3 $134.32   4.249%   $140.0273   $140.03   $140.05   $140.00  
  Purchase #4 $98.54   12.142%   $110.5047   $110.50   $110.50   $110.50  
  Purchase #5 $12.35   6.659%   $13.1724   $13.17   $13.15   $13.20  
  Purchase #6 $219.75   5.165%   $231.1001   $231.10   $231.10   $231.10  
  Purchase #7 $160.97   12.162%   $180.5472   $180.55   $180.55   $180.50  
  7 purchase totals = $788.14       $848.8877   $848.89   $848.90   $848.90