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 $216.26   12.260%   $242.7735   $242.77   $242.75   $242.80  
  Purchase #2 $211.37   4.322%   $220.5054   $220.51   $220.50   $220.50  
  Purchase #3 $249.87   12.454%   $280.9888   $280.99   $281.00   $281.00  
  Purchase #4 $65.70   13.232%   $74.3934   $74.39   $74.40   $74.40  
  Purchase #5 $33.35   4.773%   $34.9418   $34.94   $34.95   $34.90  
  Purchase #6 $101.85   12.112%   $114.1861   $114.19   $114.20   $114.20  
  Purchase #7 $56.57   6.130%   $60.0377   $60.04   $60.05   $60.00  
  7 purchase totals = $934.97       $1,027.8267   $1,027.83   $1,027.85   $1,027.80