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 $225.84   11.673%   $252.2023   $252.20   $252.20   $252.20  
  Purchase #2 $224.73   6.698%   $239.7824   $239.78   $239.80   $239.80  
  Purchase #3 $51.97   13.859%   $59.1725   $59.17   $59.15   $59.20  
  Purchase #4 $79.49   9.182%   $86.7888   $86.79   $86.80   $86.80  
  Purchase #5 $119.90   12.479%   $134.8623   $134.86   $134.85   $134.90  
  Purchase #6 $154.48   9.557%   $169.2437   $169.24   $169.25   $169.20  
  Purchase #7 $241.51   9.298%   $263.9656   $263.97   $263.95   $264.00  
  7 purchase totals = $1,097.92       $1,206.0176   $1,206.01   $1,206.00   $1,206.10