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 $8.95   7.201%   $9.5945   $9.59   $9.60   $9.60  
  Purchase #2 $231.84   7.242%   $248.6299   $248.63   $248.65   $248.60  
  Purchase #3 $22.89   4.667%   $23.9583   $23.96   $23.95   $24.00  
  Purchase #4 $48.30   3.356%   $49.9209   $49.92   $49.90   $49.90  
  Purchase #5 $49.64   6.168%   $52.7018   $52.70   $52.70   $52.70  
  Purchase #6 $236.65   12.277%   $265.7035   $265.70   $265.70   $265.70  
  Purchase #7 $160.89   8.339%   $174.3066   $174.31   $174.30   $174.30  
  7 purchase totals = $759.16       $824.8155   $824.81   $824.80   $824.80