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 $57.82   9.658%   $63.4043   $63.40   $63.40   $63.40  
  Purchase #2 $227.41   13.760%   $258.7016   $258.70   $258.70   $258.70  
  Purchase #3 $184.86   8.588%   $200.7358   $200.74   $200.75   $200.70  
  Purchase #4 $141.30   3.708%   $146.5394   $146.54   $146.55   $146.50  
  Purchase #5 $208.97   3.104%   $215.4564   $215.46   $215.45   $215.50  
  Purchase #6 $11.61   12.678%   $13.0819   $13.08   $13.10   $13.10  
  Purchase #7 $79.75   10.238%   $87.9148   $87.91   $87.90   $87.90  
  7 purchase totals = $911.72       $985.8342   $985.83   $985.85   $985.80