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 $60.91   13.127%   $68.9057   $68.91   $68.90   $68.90  
  Purchase #2 $124.93   9.398%   $136.6709   $136.67   $136.65   $136.70  
  Purchase #3 $12.32   11.654%   $13.7558   $13.76   $13.75   $13.80  
  Purchase #4 $21.48   8.318%   $23.2667   $23.27   $23.25   $23.30  
  Purchase #5 $49.88   7.708%   $53.7248   $53.72   $53.70   $53.70  
  Purchase #6 $17.90   4.444%   $18.6955   $18.70   $18.70   $18.70  
  Purchase #7 $105.41   10.188%   $116.1492   $116.15   $116.15   $116.10  
  7 purchase totals = $392.83       $431.1686   $431.18   $431.10   $431.20