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 $140.51   12.839%   $158.5501   $158.55   $158.55   $158.60  
  Purchase #2 $124.82   11.125%   $138.7062   $138.71   $138.70   $138.70  
  Purchase #3 $162.87   12.106%   $182.587   $182.59   $182.60   $182.60  
  Purchase #4 $211.93   10.743%   $234.6976   $234.70   $234.70   $234.70  
  Purchase #5 $155.74   11.780%   $174.0862   $174.09   $174.10   $174.10  
  Purchase #6 $199.47   9.593%   $218.6052   $218.61   $218.60   $218.60  
  Purchase #7 $202.62   7.290%   $217.391   $217.39   $217.40   $217.40  
  7 purchase totals = $1,197.96       $1,324.6233   $1,324.64   $1,324.65   $1,324.70