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 $88.61   8.759%   $96.3713   $96.37   $96.35   $96.40  
  Purchase #2 $41.87   3.594%   $43.3748   $43.37   $43.35   $43.40  
  Purchase #3 $122.46   5.626%   $129.3496   $129.35   $129.35   $129.30  
  Purchase #4 $121.91   7.352%   $130.8728   $130.87   $130.85   $130.90  
  Purchase #5 $121.32   6.628%   $129.3611   $129.36   $129.35   $129.40  
  Purchase #6 $19.91   10.656%   $22.0316   $22.03   $22.05   $22.00  
  Purchase #7 $156.91   5.697%   $165.8492   $165.85   $165.85   $165.80  
  7 purchase totals = $672.99       $717.2104   $717.20   $717.15   $717.20