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 $162.58   13.342%   $184.2714   $184.27   $184.25   $184.30  
  Purchase #2 $33.45   4.485%   $34.9502   $34.95   $34.95   $35.00  
  Purchase #3 $112.54   8.583%   $122.1993   $122.20   $122.20   $122.20  
  Purchase #4 $184.95   13.435%   $209.798   $209.80   $209.80   $209.80  
  Purchase #5 $221.38   8.233%   $239.6062   $239.61   $239.60   $239.60  
  Purchase #6 $173.58   9.263%   $189.6587   $189.66   $189.65   $189.70  
  Purchase #7 $91.43   3.477%   $94.609   $94.61   $94.60   $94.60  
  7 purchase totals = $979.91       $1,075.0928   $1,075.10   $1,075.05   $1,075.20