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 $227.40   8.703%   $247.1906   $247.19   $247.20   $247.20  
  Purchase #2 $219.99   8.455%   $238.5902   $238.59   $238.60   $238.60  
  Purchase #3 $96.60   6.593%   $102.9688   $102.97   $102.95   $103.00  
  Purchase #4 $65.82   3.117%   $67.8716   $67.87   $67.85   $67.90  
  Purchase #5 $248.54   7.227%   $266.502   $266.50   $266.50   $266.50  
  Purchase #6 $46.80   13.166%   $52.9617   $52.96   $52.95   $53.00  
  Purchase #7 $222.48   5.329%   $234.336   $234.34   $234.35   $234.30  
  7 purchase totals = $1,127.63       $1,210.4209   $1,210.42   $1,210.40   $1,210.50