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 $116.37   6.206%   $123.5919   $123.59   $123.60   $123.60  
  Purchase #2 $25.27   3.721%   $26.2103   $26.21   $26.20   $26.20  
  Purchase #3 $129.61   11.181%   $144.1017   $144.10   $144.10   $144.10  
  Purchase #4 $197.76   13.457%   $224.3726   $224.37   $224.35   $224.40  
  Purchase #5 $216.56   5.161%   $227.7367   $227.74   $227.75   $227.70  
  Purchase #6 $214.54   11.455%   $239.1156   $239.12   $239.10   $239.10  
  Purchase #7 $45.75   10.572%   $50.5867   $50.59   $50.60   $50.60  
  7 purchase totals = $945.86       $1,035.7155   $1,035.72   $1,035.70   $1,035.70