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 $87.84   5.641%   $92.7951   $92.80   $92.80   $92.80  
  Purchase #2 $173.89   10.707%   $192.5084   $192.51   $192.50   $192.50  
  Purchase #3 $232.35   5.872%   $245.9936   $245.99   $246.00   $246.00  
  Purchase #4 $248.36   6.782%   $265.2038   $265.20   $265.20   $265.20  
  Purchase #5 $11.63   7.226%   $12.4704   $12.47   $12.45   $12.50  
  Purchase #6 $165.60   4.551%   $173.1365   $173.14   $173.15   $173.10  
  Purchase #7 $10.77   12.256%   $12.09   $12.09   $12.10   $12.10  
  7 purchase totals = $930.44       $994.1978   $994.20   $994.20   $994.20