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 $226.65   11.447%   $252.5946   $252.59   $252.60   $252.60  
  Purchase #2 $192.63   13.618%   $218.8624   $218.86   $218.85   $218.90  
  Purchase #3 $69.42   13.661%   $78.9035   $78.90   $78.90   $78.90  
  Purchase #4 $240.40   10.164%   $264.8343   $264.83   $264.85   $264.80  
  Purchase #5 $190.75   3.409%   $197.2527   $197.25   $197.25   $197.30  
  Purchase #6 $195.30   3.399%   $201.9382   $201.94   $201.95   $201.90  
  Purchase #7 $26.27   12.584%   $29.5758   $29.58   $29.60   $29.60  
  7 purchase totals = $1,141.42       $1,243.9615   $1,243.95   $1,244.00   $1,244.00