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 $215.49   3.773%   $223.6204   $223.62   $223.60   $223.60  
  Purchase #2 $118.94   9.624%   $130.3868   $130.39   $130.40   $130.40  
  Purchase #3 $145.90   8.331%   $158.0549   $158.05   $158.05   $158.10  
  Purchase #4 $221.65   7.473%   $238.2139   $238.21   $238.20   $238.20  
  Purchase #5 $233.80   8.507%   $253.6894   $253.69   $253.70   $253.70  
  Purchase #6 $191.37   5.653%   $202.1881   $202.19   $202.20   $202.20  
  Purchase #7 $56.29   6.296%   $59.834   $59.83   $59.85   $59.80  
  7 purchase totals = $1,183.44       $1,265.9875   $1,265.98   $1,266.00   $1,266.00