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 $238.62   3.758%   $247.5873   $247.59   $247.60   $247.60  
  Purchase #2 $205.73   13.518%   $233.5406   $233.54   $233.55   $233.50  
  Purchase #3 $243.66   13.142%   $275.6818   $275.68   $275.70   $275.70  
  Purchase #4 $116.61   6.525%   $124.2188   $124.22   $124.20   $124.20  
  Purchase #5 $27.60   11.500%   $30.774   $30.77   $30.75   $30.80  
  Purchase #6 $215.92   8.286%   $233.8111   $233.81   $233.80   $233.80  
  Purchase #7 $17.25   5.184%   $18.1442   $18.14   $18.15   $18.10  
  7 purchase totals = $1,065.39       $1,163.7578   $1,163.75   $1,163.75   $1,163.70