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 $55.27   7.570%   $59.4539   $59.45   $59.45   $59.50  
  Purchase #2 $217.54   8.598%   $236.2441   $236.24   $236.25   $236.20  
  Purchase #3 $184.97   9.394%   $202.3461   $202.35   $202.35   $202.30  
  Purchase #4 $223.31   11.221%   $248.3676   $248.37   $248.35   $248.40  
  Purchase #5 $163.61   7.303%   $175.5584   $175.56   $175.55   $175.60  
  Purchase #6 $47.77   3.220%   $49.3082   $49.31   $49.30   $49.30  
  Purchase #7 $9.91   10.411%   $10.9417   $10.94   $10.95   $10.90  
  7 purchase totals = $902.38       $982.2200   $982.22   $982.20   $982.20