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 $214.69   13.488%   $243.6474   $243.65   $243.65   $243.60  
  Purchase #2 $100.88   7.786%   $108.7345   $108.73   $108.75   $108.70  
  Purchase #3 $136.65   7.558%   $146.978   $146.98   $147.00   $147.00  
  Purchase #4 $26.92   9.272%   $29.416   $29.42   $29.40   $29.40  
  Purchase #5 $88.52   5.836%   $93.686   $93.69   $93.70   $93.70  
  Purchase #6 $70.31   6.454%   $74.8478   $74.85   $74.85   $74.80  
  Purchase #7 $239.68   8.475%   $259.9929   $259.99   $260.00   $260.00  
  7 purchase totals = $877.65       $957.3026   $957.31   $957.35   $957.20