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 $222.72   8.613%   $241.9029   $241.90   $241.90   $241.90  
  Purchase #2 $152.82   9.466%   $167.2859   $167.29   $167.30   $167.30  
  Purchase #3 $106.99   11.289%   $119.0681   $119.07   $119.05   $119.10  
  Purchase #4 $63.88   10.317%   $70.4705   $70.47   $70.45   $70.50  
  Purchase #5 $193.81   6.551%   $206.5065   $206.51   $206.50   $206.50  
  Purchase #6 $65.37   4.479%   $68.2979   $68.30   $68.30   $68.30  
  Purchase #7 $106.77   5.621%   $112.7715   $112.77   $112.75   $112.80  
  7 purchase totals = $912.36       $986.3033   $986.31   $986.25   $986.40