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 $95.89   12.204%   $107.5924   $107.59   $107.60   $107.60  
  Purchase #2 $33.50   12.215%   $37.592   $37.59   $37.60   $37.60  
  Purchase #3 $118.40   12.784%   $133.5363   $133.54   $133.55   $133.50  
  Purchase #4 $53.62   13.208%   $60.7021   $60.70   $60.70   $60.70  
  Purchase #5 $234.26   12.500%   $263.5425   $263.54   $263.55   $263.50  
  Purchase #6 $200.91   7.103%   $215.1806   $215.18   $215.20   $215.20  
  Purchase #7 $66.48   5.163%   $69.9124   $69.91   $69.90   $69.90  
  7 purchase totals = $803.06       $888.0583   $888.05   $888.10   $888.00