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 $92.69   3.265%   $95.7163   $95.72   $95.70   $95.70  
  Purchase #2 $187.70   6.332%   $199.5852   $199.59   $199.60   $199.60  
  Purchase #3 $23.98   8.148%   $25.9339   $25.93   $25.95   $25.90  
  Purchase #4 $154.57   4.681%   $161.8054   $161.81   $161.80   $161.80  
  Purchase #5 $219.66   7.856%   $236.9165   $236.92   $236.90   $236.90  
  Purchase #6 $234.60   12.382%   $263.6482   $263.65   $263.65   $263.60  
  Purchase #7 $5.31   3.242%   $5.4822   $5.48   $5.50   $5.50  
  7 purchase totals = $918.51       $989.0877   $989.10   $989.10   $989.00