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 $53.93   11.145%   $59.9405   $59.94   $59.95   $59.90  
  Purchase #2 $81.85   3.814%   $84.9718   $84.97   $84.95   $85.00  
  Purchase #3 $84.74   10.122%   $93.3174   $93.32   $93.30   $93.30  
  Purchase #4 $232.65   9.523%   $254.8053   $254.81   $254.80   $254.80  
  Purchase #5 $14.89   11.230%   $16.5621   $16.56   $16.55   $16.60  
  Purchase #6 $124.98   7.181%   $133.9548   $133.95   $133.95   $134.00  
  Purchase #7 $87.77   5.433%   $92.5385   $92.54   $92.55   $92.50  
  7 purchase totals = $680.81       $736.0904   $736.09   $736.05   $736.10