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 $90.85   5.153%   $95.5315   $95.53   $95.55   $95.50  
  Purchase #2 $146.29   11.813%   $163.5712   $163.57   $163.55   $163.60  
  Purchase #3 $67.64   7.798%   $72.9146   $72.91   $72.90   $72.90  
  Purchase #4 $142.78   5.695%   $150.9113   $150.91   $150.90   $150.90  
  Purchase #5 $65.76   4.744%   $68.8797   $68.88   $68.90   $68.90  
  Purchase #6 $23.83   9.337%   $26.055   $26.06   $26.05   $26.10  
  Purchase #7 $125.35   7.636%   $134.9217   $134.92   $134.90   $134.90  
  7 purchase totals = $662.50       $712.7850   $712.78   $712.75   $712.80