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 $98.64   5.762%   $104.3236   $104.32   $104.30   $104.30  
  Purchase #2 $69.83   3.539%   $72.3013   $72.30   $72.30   $72.30  
  Purchase #3 $134.95   10.296%   $148.8445   $148.84   $148.85   $148.80  
  Purchase #4 $147.64   9.609%   $161.8267   $161.83   $161.85   $161.80  
  Purchase #5 $225.87   12.349%   $253.7627   $253.76   $253.75   $253.80  
  Purchase #6 $153.58   5.601%   $162.182   $162.18   $162.20   $162.20  
  Purchase #7 $141.48   13.599%   $160.7199   $160.72   $160.70   $160.70  
  7 purchase totals = $971.99       $1,063.9607   $1,063.95   $1,063.95   $1,063.90