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 $222.99   7.481%   $239.6719   $239.67   $239.65   $239.70  
  Purchase #2 $60.32   8.841%   $65.6529   $65.65   $65.65   $65.70  
  Purchase #3 $169.50   3.531%   $175.485   $175.49   $175.50   $175.50  
  Purchase #4 $96.49   8.571%   $104.7602   $104.76   $104.75   $104.80  
  Purchase #5 $77.40   12.695%   $87.2259   $87.23   $87.25   $87.20  
  Purchase #6 $10.73   10.799%   $11.8887   $11.89   $11.90   $11.90  
  Purchase #7 $234.94   13.222%   $266.0038   $266.00   $266.00   $266.00  
  7 purchase totals = $872.37       $950.6884   $950.69   $950.70   $950.80