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 $85.93   7.275%   $92.1814   $92.18   $92.20   $92.20  
  Purchase #2 $107.62   7.621%   $115.8217   $115.82   $115.80   $115.80  
  Purchase #3 $239.95   11.621%   $267.8346   $267.83   $267.85   $267.80  
  Purchase #4 $52.43   11.812%   $58.623   $58.62   $58.60   $58.60  
  Purchase #5 $231.76   13.339%   $262.6745   $262.67   $262.65   $262.70  
  Purchase #6 $52.34   6.815%   $55.907   $55.91   $55.90   $55.90  
  Purchase #7 $173.81   7.327%   $186.5451   $186.55   $186.55   $186.50  
  7 purchase totals = $943.84       $1,039.5873   $1,039.58   $1,039.55   $1,039.50