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 $246.91   5.199%   $259.7469   $259.75   $259.75   $259.70  
  Purchase #2 $47.89   4.655%   $50.1193   $50.12   $50.10   $50.10  
  Purchase #3 $58.63   4.310%   $61.157   $61.16   $61.15   $61.20  
  Purchase #4 $81.59   8.827%   $88.7919   $88.79   $88.80   $88.80  
  Purchase #5 $236.47   3.504%   $244.7559   $244.76   $244.75   $244.80  
  Purchase #6 $47.39   9.477%   $51.8812   $51.88   $51.90   $51.90  
  Purchase #7 $17.57   11.682%   $19.6225   $19.62   $19.60   $19.60  
  7 purchase totals = $736.45       $776.0747   $776.08   $776.05   $776.10