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 $214.66   7.151%   $230.0103   $230.01   $230.00   $230.00  
  Purchase #2 $84.37   5.129%   $88.6973   $88.70   $88.70   $88.70  
  Purchase #3 $107.58   7.393%   $115.5334   $115.53   $115.55   $115.50  
  Purchase #4 $112.35   12.845%   $126.7814   $126.78   $126.80   $126.80  
  Purchase #5 $95.74   6.703%   $102.1575   $102.16   $102.15   $102.20  
  Purchase #6 $119.30   10.451%   $131.768   $131.77   $131.75   $131.80  
  Purchase #7 $106.67   8.761%   $116.0154   $116.02   $116.00   $116.00  
  7 purchase totals = $840.67       $910.9633   $910.97   $910.95   $911.00