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 $232.85   8.318%   $252.2185   $252.22   $252.20   $252.20  
  Purchase #2 $210.39   5.847%   $222.6915   $222.69   $222.70   $222.70  
  Purchase #3 $111.67   5.620%   $117.9459   $117.95   $117.95   $117.90  
  Purchase #4 $74.98   3.123%   $77.3216   $77.32   $77.30   $77.30  
  Purchase #5 $111.94   10.648%   $123.8594   $123.86   $123.85   $123.90  
  Purchase #6 $44.46   6.671%   $47.4259   $47.43   $47.45   $47.40  
  Purchase #7 $185.27   4.547%   $193.6942   $193.69   $193.70   $193.70  
  7 purchase totals = $971.56       $1,035.1570   $1,035.16   $1,035.15   $1,035.10