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 $247.78   13.651%   $281.6044   $281.60   $281.60   $281.60  
  Purchase #2 $183.37   7.185%   $196.5451   $196.55   $196.55   $196.50  
  Purchase #3 $23.78   10.297%   $26.2286   $26.23   $26.25   $26.20  
  Purchase #4 $102.84   6.863%   $109.8979   $109.90   $109.90   $109.90  
  Purchase #5 $212.96   8.794%   $231.6877   $231.69   $231.70   $231.70  
  Purchase #6 $118.29   6.452%   $125.9221   $125.92   $125.90   $125.90  
  Purchase #7 $23.44   6.262%   $24.9078   $24.91   $24.90   $24.90  
  7 purchase totals = $912.46       $996.7936   $996.80   $996.80   $996.70