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 $167.53   11.484%   $186.7691   $186.77   $186.75   $186.80  
  Purchase #2 $116.48   13.361%   $132.0429   $132.04   $132.05   $132.00  
  Purchase #3 $189.38   8.653%   $205.7671   $205.77   $205.75   $205.80  
  Purchase #4 $153.59   8.676%   $166.9155   $166.92   $166.90   $166.90  
  Purchase #5 $56.90   8.815%   $61.9157   $61.92   $61.90   $61.90  
  Purchase #6 $249.97   4.818%   $262.0136   $262.01   $262.00   $262.00  
  Purchase #7 $18.65   13.492%   $21.1663   $21.17   $21.15   $21.20  
  7 purchase totals = $952.50       $1,036.5902   $1,036.60   $1,036.50   $1,036.60