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 $159.66   10.234%   $175.9996   $176.00   $176.00   $176.00  
  Purchase #2 $58.42   7.164%   $62.6052   $62.61   $62.60   $62.60  
  Purchase #3 $244.25   12.505%   $274.7935   $274.79   $274.80   $274.80  
  Purchase #4 $165.41   10.743%   $183.18   $183.18   $183.20   $183.20  
  Purchase #5 $233.66   8.271%   $252.986   $252.99   $253.00   $253.00  
  Purchase #6 $179.62   13.515%   $203.8956   $203.90   $203.90   $203.90  
  Purchase #7 $153.51   7.843%   $165.5498   $165.55   $165.55   $165.50  
  7 purchase totals = $1,194.53       $1,319.0097   $1,319.02   $1,319.05   $1,319.00