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 $224.34   13.237%   $254.0359   $254.04   $254.05   $254.00  
  Purchase #2 $177.61   6.766%   $189.6271   $189.63   $189.65   $189.60  
  Purchase #3 $110.41   11.256%   $122.8377   $122.84   $122.85   $122.80  
  Purchase #4 $72.79   4.360%   $75.9636   $75.96   $75.95   $76.00  
  Purchase #5 $21.41   12.788%   $24.1479   $24.15   $24.15   $24.10  
  Purchase #6 $86.83   6.160%   $92.1787   $92.18   $92.20   $92.20  
  Purchase #7 $230.99   7.764%   $248.9241   $248.92   $248.90   $248.90  
  7 purchase totals = $924.38       $1,007.7150   $1,007.72   $1,007.75   $1,007.60