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 $227.42   11.790%   $254.2328   $254.23   $254.25   $254.20  
  Purchase #2 $120.31   9.496%   $131.7346   $131.73   $131.75   $131.70  
  Purchase #3 $86.85   12.262%   $97.4995   $97.50   $97.50   $97.50  
  Purchase #4 $34.95   4.700%   $36.5927   $36.59   $36.60   $36.60  
  Purchase #5 $195.92   5.625%   $206.9405   $206.94   $206.95   $206.90  
  Purchase #6 $248.98   4.196%   $259.4272   $259.43   $259.45   $259.40  
  Purchase #7 $224.25   7.711%   $241.5419   $241.54   $241.55   $241.50  
  7 purchase totals = $1,138.68       $1,227.9692   $1,227.96   $1,228.05   $1,227.80