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 $222.95   13.793%   $253.7015   $253.70   $253.70   $253.70  
  Purchase #2 $180.84   8.383%   $195.9998   $196.00   $196.00   $196.00  
  Purchase #3 $77.92   4.632%   $81.5293   $81.53   $81.55   $81.50  
  Purchase #4 $133.40   4.721%   $139.6978   $139.70   $139.70   $139.70  
  Purchase #5 $103.54   9.195%   $113.0605   $113.06   $113.05   $113.10  
  Purchase #6 $6.37   11.406%   $7.0966   $7.10   $7.10   $7.10  
  Purchase #7 $231.51   4.282%   $241.4233   $241.42   $241.40   $241.40  
  7 purchase totals = $956.53       $1,032.5088   $1,032.51   $1,032.50   $1,032.50