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 $233.53   7.296%   $250.5683   $250.57   $250.55   $250.60  
  Purchase #2 $32.89   6.129%   $34.9058   $34.91   $34.90   $34.90  
  Purchase #3 $141.76   4.408%   $148.0088   $148.01   $148.00   $148.00  
  Purchase #4 $212.93   13.600%   $241.8885   $241.89   $241.90   $241.90  
  Purchase #5 $151.82   3.406%   $156.991   $156.99   $157.00   $157.00  
  Purchase #6 $162.99   6.866%   $174.1809   $174.18   $174.20   $174.20  
  Purchase #7 $126.60   11.275%   $140.8742   $140.87   $140.85   $140.90  
  7 purchase totals = $1,062.52       $1,147.4175   $1,147.42   $1,147.40   $1,147.50