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 $101.51   13.570%   $115.2849   $115.28   $115.30   $115.30  
  Purchase #2 $208.52   11.827%   $233.1817   $233.18   $233.20   $233.20  
  Purchase #3 $227.77   6.513%   $242.6047   $242.60   $242.60   $242.60  
  Purchase #4 $60.81   4.121%   $63.316   $63.32   $63.30   $63.30  
  Purchase #5 $144.70   7.362%   $155.3528   $155.35   $155.35   $155.40  
  Purchase #6 $194.77   6.769%   $207.954   $207.95   $207.95   $208.00  
  Purchase #7 $194.59   11.355%   $216.6857   $216.69   $216.70   $216.70  
  7 purchase totals = $1,132.67       $1,234.3798   $1,234.37   $1,234.40   $1,234.50