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 $248.53   9.751%   $272.7642   $272.76   $272.75   $272.80  
  Purchase #2 $217.83   3.712%   $225.9158   $225.92   $225.90   $225.90  
  Purchase #3 $44.64   13.646%   $50.7316   $50.73   $50.75   $50.70  
  Purchase #4 $29.40   9.245%   $32.118   $32.12   $32.10   $32.10  
  Purchase #5 $179.57   4.703%   $188.0152   $188.02   $188.00   $188.00  
  Purchase #6 $244.60   8.399%   $265.144   $265.14   $265.15   $265.10  
  Purchase #7 $216.37   8.372%   $234.4845   $234.48   $234.50   $234.50  
  7 purchase totals = $1,180.94       $1,269.1733   $1,269.17   $1,269.15   $1,269.10