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 $70.68   4.442%   $73.8196   $73.82   $73.80   $73.80  
  Purchase #2 $217.89   10.273%   $240.2738   $240.27   $240.25   $240.30  
  Purchase #3 $50.68   11.211%   $56.3617   $56.36   $56.35   $56.40  
  Purchase #4 $236.97   10.713%   $262.3566   $262.36   $262.35   $262.40  
  Purchase #5 $7.62   11.445%   $8.4921   $8.49   $8.50   $8.50  
  Purchase #6 $62.73   13.697%   $71.3221   $71.32   $71.30   $71.30  
  Purchase #7 $34.69   5.410%   $36.5667   $36.57   $36.55   $36.60  
  7 purchase totals = $681.26       $749.1926   $749.19   $749.10   $749.30