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 $56.99   5.609%   $60.1866   $60.19   $60.20   $60.20  
  Purchase #2 $30.43   13.193%   $34.4446   $34.44   $34.45   $34.40  
  Purchase #3 $212.84   5.353%   $224.2333   $224.23   $224.25   $224.20  
  Purchase #4 $175.57   13.291%   $198.905   $198.91   $198.90   $198.90  
  Purchase #5 $75.56   9.228%   $82.5327   $82.53   $82.55   $82.50  
  Purchase #6 $241.34   9.382%   $263.9825   $263.98   $264.00   $264.00  
  Purchase #7 $121.35   10.657%   $134.2823   $134.28   $134.30   $134.30  
  7 purchase totals = $914.08       $998.5670   $998.56   $998.65   $998.50