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 $98.67   6.466%   $105.05   $105.05   $105.05   $105.10  
  Purchase #2 $152.60   8.147%   $165.0323   $165.03   $165.05   $165.00  
  Purchase #3 $70.47   7.737%   $75.9223   $75.92   $75.90   $75.90  
  Purchase #4 $73.81   3.821%   $76.6303   $76.63   $76.65   $76.60  
  Purchase #5 $85.80   12.331%   $96.38   $96.38   $96.40   $96.40  
  Purchase #6 $80.81   13.274%   $91.5367   $91.54   $91.55   $91.50  
  Purchase #7 $188.87   5.721%   $199.6753   $199.68   $199.70   $199.70  
  7 purchase totals = $751.03       $810.2269   $810.23   $810.30   $810.20