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 $65.86   5.268%   $69.3295   $69.33   $69.35   $69.30  
  Purchase #2 $84.25   9.146%   $91.9555   $91.96   $91.95   $92.00  
  Purchase #3 $189.48   6.549%   $201.889   $201.89   $201.90   $201.90  
  Purchase #4 $88.46   9.617%   $96.9672   $96.97   $96.95   $97.00  
  Purchase #5 $73.77   7.572%   $79.3559   $79.36   $79.35   $79.40  
  Purchase #6 $73.62   3.796%   $76.4146   $76.41   $76.40   $76.40  
  Purchase #7 $206.98   10.710%   $229.1476   $229.15   $229.15   $229.10  
  7 purchase totals = $782.42       $845.0593   $845.07   $845.05   $845.10