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 $40.45   12.777%   $45.6183   $45.62   $45.60   $45.60  
  Purchase #2 $157.50   3.535%   $163.0676   $163.07   $163.05   $163.10  
  Purchase #3 $81.71   6.348%   $86.897   $86.90   $86.90   $86.90  
  Purchase #4 $245.68   3.489%   $254.2518   $254.25   $254.25   $254.30  
  Purchase #5 $182.52   13.850%   $207.799   $207.80   $207.80   $207.80  
  Purchase #6 $235.47   11.154%   $261.7343   $261.73   $261.75   $261.70  
  Purchase #7 $245.51   3.541%   $254.2035   $254.20   $254.20   $254.20  
  7 purchase totals = $1,188.84       $1,273.5715   $1,273.57   $1,273.55   $1,273.60