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 $81.68   6.756%   $87.1983   $87.20   $87.20   $87.20  
  Purchase #2 $175.44   4.763%   $183.7962   $183.80   $183.80   $183.80  
  Purchase #3 $23.78   9.302%   $25.992   $25.99   $26.00   $26.00  
  Purchase #4 $214.49   5.641%   $226.5894   $226.59   $226.60   $226.60  
  Purchase #5 $220.60   5.710%   $233.1963   $233.20   $233.20   $233.20  
  Purchase #6 $224.38   13.483%   $254.6332   $254.63   $254.65   $254.60  
  Purchase #7 $191.80   8.115%   $207.3646   $207.36   $207.35   $207.40  
  7 purchase totals = $1,132.17       $1,218.7700   $1,218.77   $1,218.80   $1,218.80