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 $227.86   11.323%   $253.6606   $253.66   $253.65   $253.70  
  Purchase #2 $114.74   11.250%   $127.6483   $127.65   $127.65   $127.60  
  Purchase #3 $47.88   4.513%   $50.0408   $50.04   $50.05   $50.00  
  Purchase #4 $44.76   10.821%   $49.6035   $49.60   $49.60   $49.60  
  Purchase #5 $231.82   9.690%   $254.2834   $254.28   $254.30   $254.30  
  Purchase #6 $125.64   7.191%   $134.6748   $134.67   $134.65   $134.70  
  Purchase #7 $29.62   11.686%   $33.0814   $33.08   $33.10   $33.10  
  7 purchase totals = $822.32       $902.9928   $902.98   $903.00   $903.00