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 $215.29   8.708%   $234.0375   $234.04   $234.05   $234.00  
  Purchase #2 $173.26   13.839%   $197.2375   $197.24   $197.25   $197.20  
  Purchase #3 $248.80   10.139%   $274.0258   $274.03   $274.05   $274.00  
  Purchase #4 $161.45   11.336%   $179.752   $179.75   $179.75   $179.80  
  Purchase #5 $67.92   11.263%   $75.5698   $75.57   $75.55   $75.60  
  Purchase #6 $30.88   11.512%   $34.4349   $34.43   $34.45   $34.40  
  Purchase #7 $34.68   11.187%   $38.5597   $38.56   $38.55   $38.60  
  7 purchase totals = $932.28       $1,033.6172   $1,033.62   $1,033.65   $1,033.60