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 $62.97   3.435%   $65.133   $65.13   $65.15   $65.10  
  Purchase #2 $222.87   4.210%   $232.2528   $232.25   $232.25   $232.30  
  Purchase #3 $10.58   11.384%   $11.7844   $11.78   $11.80   $11.80  
  Purchase #4 $35.88   10.728%   $39.7292   $39.73   $39.75   $39.70  
  Purchase #5 $243.53   11.141%   $270.6617   $270.66   $270.65   $270.70  
  Purchase #6 $131.64   13.149%   $148.9493   $148.95   $148.95   $148.90  
  Purchase #7 $220.70   12.558%   $248.4155   $248.42   $248.40   $248.40  
  7 purchase totals = $928.17       $1,016.9259   $1,016.92   $1,016.95   $1,016.90