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 $216.66   13.103%   $245.049   $245.05   $245.05   $245.00  
  Purchase #2 $250.47   12.170%   $280.9522   $280.95   $280.95   $281.00  
  Purchase #3 $120.57   4.703%   $126.2404   $126.24   $126.25   $126.20  
  Purchase #4 $219.45   11.275%   $244.193   $244.19   $244.20   $244.20  
  Purchase #5 $34.33   13.191%   $38.8585   $38.86   $38.85   $38.90  
  Purchase #6 $39.81   7.849%   $42.9347   $42.93   $42.95   $42.90  
  Purchase #7 $164.61   7.290%   $176.6101   $176.61   $176.60   $176.60  
  7 purchase totals = $1,045.90       $1,154.8379   $1,154.83   $1,154.85   $1,154.80