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 $205.95   5.307%   $216.8798   $216.88   $216.90   $216.90  
  Purchase #2 $14.83   13.214%   $16.7896   $16.79   $16.80   $16.80  
  Purchase #3 $46.34   4.650%   $48.4948   $48.49   $48.50   $48.50  
  Purchase #4 $245.79   11.874%   $274.9751   $274.98   $275.00   $275.00  
  Purchase #5 $218.98   10.795%   $242.6189   $242.62   $242.60   $242.60  
  Purchase #6 $58.77   11.669%   $65.6279   $65.63   $65.65   $65.60  
  Purchase #7 $243.71   6.318%   $259.1076   $259.11   $259.10   $259.10  
  7 purchase totals = $1,034.37       $1,124.4937   $1,124.50   $1,124.55   $1,124.50