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 $208.40   13.705%   $236.9612   $236.96   $236.95   $237.00  
  Purchase #2 $47.98   11.167%   $53.3379   $53.34   $53.35   $53.30  
  Purchase #3 $242.28   8.199%   $262.1445   $262.14   $262.15   $262.10  
  Purchase #4 $86.73   4.867%   $90.9511   $90.95   $90.95   $91.00  
  Purchase #5 $241.45   10.428%   $266.6284   $266.63   $266.65   $266.60  
  Purchase #6 $106.39   4.677%   $111.3659   $111.37   $111.35   $111.40  
  Purchase #7 $53.33   3.355%   $55.1192   $55.12   $55.10   $55.10  
  7 purchase totals = $986.56       $1,076.5082   $1,076.51   $1,076.50   $1,076.50