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 $47.65   13.796%   $54.2238   $54.22   $54.20   $54.20  
  Purchase #2 $38.66   11.232%   $43.0023   $43.00   $43.00   $43.00  
  Purchase #3 $82.38   11.599%   $91.9353   $91.94   $91.95   $91.90  
  Purchase #4 $89.43   7.339%   $95.9933   $95.99   $96.00   $96.00  
  Purchase #5 $153.73   6.210%   $163.2766   $163.28   $163.30   $163.30  
  Purchase #6 $239.82   7.827%   $258.5907   $258.59   $258.60   $258.60  
  Purchase #7 $185.38   8.408%   $200.9668   $200.97   $200.95   $201.00  
  7 purchase totals = $837.05       $907.9888   $907.99   $908.00   $908.00