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 $249.99   8.479%   $271.1867   $271.19   $271.20   $271.20  
  Purchase #2 $86.91   7.273%   $93.231   $93.23   $93.25   $93.20  
  Purchase #3 $60.32   3.583%   $62.4813   $62.48   $62.50   $62.50  
  Purchase #4 $185.79   6.412%   $197.7029   $197.70   $197.70   $197.70  
  Purchase #5 $215.57   5.114%   $226.5942   $226.59   $226.60   $226.60  
  Purchase #6 $107.85   5.517%   $113.8001   $113.80   $113.80   $113.80  
  Purchase #7 $58.96   4.484%   $61.6038   $61.60   $61.60   $61.60  
  7 purchase totals = $965.39       $1,026.6000   $1,026.59   $1,026.65   $1,026.60