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 $186.73   3.446%   $193.1647   $193.16   $193.15   $193.20  
  Purchase #2 $208.74   7.662%   $224.7337   $224.73   $224.75   $224.70  
  Purchase #3 $24.32   6.749%   $25.9614   $25.96   $25.95   $26.00  
  Purchase #4 $205.81   5.234%   $216.5821   $216.58   $216.60   $216.60  
  Purchase #5 $27.86   10.664%   $30.831   $30.83   $30.85   $30.80  
  Purchase #6 $87.97   6.167%   $93.3951   $93.40   $93.40   $93.40  
  Purchase #7 $152.25   12.415%   $171.1518   $171.15   $171.15   $171.20  
  7 purchase totals = $893.68       $955.8198   $955.81   $955.85   $955.90