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 $56.91   13.555%   $64.6242   $64.62   $64.60   $64.60  
  Purchase #2 $81.87   5.265%   $86.1805   $86.18   $86.20   $86.20  
  Purchase #3 $206.72   4.701%   $216.4379   $216.44   $216.45   $216.40  
  Purchase #4 $51.75   11.665%   $57.7866   $57.79   $57.80   $57.80  
  Purchase #5 $115.55   9.126%   $126.0951   $126.10   $126.10   $126.10  
  Purchase #6 $188.63   11.572%   $210.4583   $210.46   $210.45   $210.50  
  Purchase #7 $224.71   7.609%   $241.8082   $241.81   $241.80   $241.80  
  7 purchase totals = $926.14       $1,003.3908   $1,003.40   $1,003.40   $1,003.40