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 $56.37   11.599%   $62.9084   $62.91   $62.90   $62.90  
  Purchase #2 $5.73   13.555%   $6.5067   $6.51   $6.50   $6.50  
  Purchase #3 $188.71   5.164%   $198.455   $198.46   $198.45   $198.50  
  Purchase #4 $33.55   10.435%   $37.0509   $37.05   $37.05   $37.10  
  Purchase #5 $211.58   8.341%   $229.2279   $229.23   $229.25   $229.20  
  Purchase #6 $68.64   12.542%   $77.2488   $77.25   $77.25   $77.20  
  Purchase #7 $204.99   4.263%   $213.7287   $213.73   $213.75   $213.70  
  7 purchase totals = $769.57       $825.1264   $825.14   $825.15   $825.10