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 $64.93   5.833%   $68.7174   $68.72   $68.70   $68.70  
  Purchase #2 $63.89   7.739%   $68.8344   $68.83   $68.85   $68.80  
  Purchase #3 $246.87   5.219%   $259.7541   $259.75   $259.75   $259.80  
  Purchase #4 $188.62   13.620%   $214.31   $214.31   $214.30   $214.30  
  Purchase #5 $249.31   7.453%   $267.8911   $267.89   $267.90   $267.90  
  Purchase #6 $97.83   13.785%   $111.3159   $111.32   $111.30   $111.30  
  Purchase #7 $231.60   13.245%   $262.2754   $262.28   $262.30   $262.30  
  7 purchase totals = $1,143.05       $1,253.0983   $1,253.10   $1,253.10   $1,253.10