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 $67.89   13.110%   $76.7904   $76.79   $76.80   $76.80  
  Purchase #2 $149.37   10.275%   $164.7178   $164.72   $164.70   $164.70  
  Purchase #3 $105.26   13.854%   $119.8427   $119.84   $119.85   $119.80  
  Purchase #4 $29.86   12.326%   $33.5405   $33.54   $33.55   $33.50  
  Purchase #5 $184.60   4.366%   $192.6596   $192.66   $192.65   $192.70  
  Purchase #6 $137.82   12.302%   $154.7746   $154.77   $154.75   $154.80  
  Purchase #7 $242.57   9.845%   $266.451   $266.45   $266.45   $266.50  
  7 purchase totals = $917.37       $1,008.7766   $1,008.77   $1,008.75   $1,008.80