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 $234.29   8.560%   $254.3452   $254.35   $254.35   $254.30  
  Purchase #2 $132.26   10.479%   $146.1195   $146.12   $146.10   $146.10  
  Purchase #3 $79.76   8.427%   $86.4814   $86.48   $86.50   $86.50  
  Purchase #4 $219.91   4.393%   $229.5706   $229.57   $229.55   $229.60  
  Purchase #5 $243.26   9.563%   $266.523   $266.52   $266.50   $266.50  
  Purchase #6 $7.89   11.836%   $8.8239   $8.82   $8.80   $8.80  
  Purchase #7 $183.80   13.389%   $208.409   $208.41   $208.40   $208.40  
  7 purchase totals = $1,101.17       $1,200.2726   $1,200.27   $1,200.20   $1,200.20