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 $96.76   5.606%   $102.1844   $102.18   $102.20   $102.20  
  Purchase #2 $144.35   6.431%   $153.6331   $153.63   $153.65   $153.60  
  Purchase #3 $67.31   6.552%   $71.7202   $71.72   $71.70   $71.70  
  Purchase #4 $195.77   7.136%   $209.7401   $209.74   $209.75   $209.70  
  Purchase #5 $55.92   5.387%   $58.9324   $58.93   $58.95   $58.90  
  Purchase #6 $9.67   5.151%   $10.1681   $10.17   $10.15   $10.20  
  Purchase #7 $64.34   7.598%   $69.2286   $69.23   $69.25   $69.20  
  7 purchase totals = $634.12       $675.6069   $675.60   $675.65   $675.50