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 $68.93   11.708%   $77.0003   $77.00   $77.00   $77.00  
  Purchase #2 $208.95   5.186%   $219.7861   $219.79   $219.80   $219.80  
  Purchase #3 $223.77   11.781%   $250.1323   $250.13   $250.15   $250.10  
  Purchase #4 $217.26   11.756%   $242.8011   $242.80   $242.80   $242.80  
  Purchase #5 $235.95   4.403%   $246.3389   $246.34   $246.35   $246.30  
  Purchase #6 $71.84   6.594%   $76.5771   $76.58   $76.60   $76.60  
  Purchase #7 $163.79   12.360%   $184.0344   $184.03   $184.05   $184.00  
  7 purchase totals = $1,190.49       $1,296.6702   $1,296.67   $1,296.75   $1,296.60