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 $203.37   7.541%   $218.7061   $218.71   $218.70   $218.70  
  Purchase #2 $117.69   12.353%   $132.2282   $132.23   $132.25   $132.20  
  Purchase #3 $40.30   7.184%   $43.1952   $43.20   $43.20   $43.20  
  Purchase #4 $174.51   4.637%   $182.602   $182.60   $182.60   $182.60  
  Purchase #5 $147.72   4.669%   $154.617   $154.62   $154.60   $154.60  
  Purchase #6 $118.32   11.704%   $132.1682   $132.17   $132.15   $132.20  
  Purchase #7 $233.85   4.495%   $244.3616   $244.36   $244.35   $244.40  
  7 purchase totals = $1,035.76       $1,107.8783   $1,107.89   $1,107.85   $1,107.90