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 $123.95   5.807%   $131.1478   $131.15   $131.15   $131.10  
  Purchase #2 $64.39   4.117%   $67.0409   $67.04   $67.05   $67.00  
  Purchase #3 $248.61   11.120%   $276.2554   $276.26   $276.25   $276.30  
  Purchase #4 $136.55   12.682%   $153.8673   $153.87   $153.85   $153.90  
  Purchase #5 $107.60   7.324%   $115.4806   $115.48   $115.50   $115.50  
  Purchase #6 $201.37   12.306%   $226.1506   $226.15   $226.15   $226.20  
  Purchase #7 $65.57   9.398%   $71.7323   $71.73   $71.75   $71.70  
  7 purchase totals = $948.04       $1,041.6749   $1,041.68   $1,041.70   $1,041.70