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 $59.41   10.436%   $65.61   $65.61   $65.60   $65.60  
  Purchase #2 $74.25   3.536%   $76.8755   $76.88   $76.90   $76.90  
  Purchase #3 $232.91   3.586%   $241.2622   $241.26   $241.25   $241.30  
  Purchase #4 $125.51   5.281%   $132.1382   $132.14   $132.15   $132.10  
  Purchase #5 $150.95   7.678%   $162.5399   $162.54   $162.55   $162.50  
  Purchase #6 $61.62   8.336%   $66.7566   $66.76   $66.75   $66.80  
  Purchase #7 $126.26   3.281%   $130.4026   $130.40   $130.40   $130.40  
  7 purchase totals = $830.91       $875.5850   $875.59   $875.60   $875.60