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 $45.41   13.830%   $51.6902   $51.69   $51.70   $51.70  
  Purchase #2 $113.75   11.257%   $126.5548   $126.55   $126.55   $126.60  
  Purchase #3 $5.63   4.196%   $5.8662   $5.87   $5.85   $5.90  
  Purchase #4 $64.28   12.454%   $72.2854   $72.29   $72.30   $72.30  
  Purchase #5 $43.39   10.797%   $48.0748   $48.07   $48.05   $48.10  
  Purchase #6 $75.29   11.760%   $84.1441   $84.14   $84.15   $84.10  
  Purchase #7 $246.88   9.164%   $269.5041   $269.50   $269.50   $269.50  
  7 purchase totals = $594.63       $658.1196   $658.11   $658.10   $658.20