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 $209.44   6.836%   $223.7573   $223.76   $223.75   $223.80  
  Purchase #2 $250.95   8.534%   $272.3661   $272.37   $272.35   $272.40  
  Purchase #3 $85.51   10.253%   $94.2773   $94.28   $94.30   $94.30  
  Purchase #4 $223.26   12.729%   $251.6788   $251.68   $251.70   $251.70  
  Purchase #5 $41.35   8.497%   $44.8635   $44.86   $44.85   $44.90  
  Purchase #6 $228.43   8.499%   $247.8443   $247.84   $247.85   $247.80  
  Purchase #7 $22.74   4.839%   $23.8404   $23.84   $23.85   $23.80  
  7 purchase totals = $1,061.68       $1,158.6277   $1,158.63   $1,158.65   $1,158.70