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 $61.38   6.599%   $65.4305   $65.43   $65.45   $65.40  
  Purchase #2 $91.77   10.807%   $101.6876   $101.69   $101.70   $101.70  
  Purchase #3 $206.52   5.147%   $217.1496   $217.15   $217.15   $217.10  
  Purchase #4 $171.34   12.497%   $192.7524   $192.75   $192.75   $192.80  
  Purchase #5 $124.56   11.634%   $139.0513   $139.05   $139.05   $139.10  
  Purchase #6 $234.87   13.582%   $266.77   $266.77   $266.75   $266.80  
  Purchase #7 $77.42   4.526%   $80.924   $80.92   $80.90   $80.90  
  7 purchase totals = $967.86       $1,063.7654   $1,063.76   $1,063.75   $1,063.80