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 $61.48   6.802%   $65.6619   $65.66   $65.65   $65.70  
  Purchase #2 $26.60   10.791%   $29.4704   $29.47   $29.45   $29.50  
  Purchase #3 $228.26   6.318%   $242.6815   $242.68   $242.70   $242.70  
  Purchase #4 $133.76   13.428%   $151.7213   $151.72   $151.70   $151.70  
  Purchase #5 $206.41   12.255%   $231.7055   $231.71   $231.70   $231.70  
  Purchase #6 $36.83   6.463%   $39.2103   $39.21   $39.20   $39.20  
  Purchase #7 $132.85   13.862%   $151.2657   $151.27   $151.25   $151.30  
  7 purchase totals = $826.19       $911.7166   $911.72   $911.65   $911.80