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 $59.88   4.527%   $62.5908   $62.59   $62.60   $62.60  
  Purchase #2 $128.47   12.732%   $144.8268   $144.83   $144.85   $144.80  
  Purchase #3 $207.70   3.285%   $214.5229   $214.52   $214.50   $214.50  
  Purchase #4 $94.63   10.742%   $104.7952   $104.80   $104.80   $104.80  
  Purchase #5 $183.80   5.327%   $193.591   $193.59   $193.60   $193.60  
  Purchase #6 $161.57   3.493%   $167.2136   $167.21   $167.20   $167.20  
  Purchase #7 $69.60   13.384%   $78.9153   $78.92   $78.90   $78.90  
  7 purchase totals = $905.65       $966.4556   $966.46   $966.45   $966.40