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 $26.78   6.569%   $28.5392   $28.54   $28.55   $28.50  
  Purchase #2 $178.28   7.575%   $191.7847   $191.78   $191.80   $191.80  
  Purchase #3 $188.77   4.657%   $197.561   $197.56   $197.55   $197.60  
  Purchase #4 $177.86   13.299%   $201.5136   $201.51   $201.50   $201.50  
  Purchase #5 $164.58   8.556%   $178.6615   $178.66   $178.65   $178.70  
  Purchase #6 $43.42   4.463%   $45.3578   $45.36   $45.35   $45.40  
  Purchase #7 $41.51   3.418%   $42.9288   $42.93   $42.95   $42.90  
  7 purchase totals = $821.20       $886.3466   $886.34   $886.35   $886.40