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 $115.94   7.324%   $124.4314   $124.43   $124.45   $124.40  
  Purchase #2 $80.33   6.749%   $85.7515   $85.75   $85.75   $85.80  
  Purchase #3 $135.62   12.564%   $152.6593   $152.66   $152.65   $152.70  
  Purchase #4 $209.81   11.498%   $233.934   $233.93   $233.95   $233.90  
  Purchase #5 $82.44   5.358%   $86.8571   $86.86   $86.85   $86.90  
  Purchase #6 $250.36   7.496%   $269.127   $269.13   $269.15   $269.10  
  Purchase #7 $203.90   6.224%   $216.5907   $216.59   $216.60   $216.60  
  7 purchase totals = $1,078.40       $1,169.3510   $1,169.35   $1,169.40   $1,169.40