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 $195.53   8.378%   $211.9115   $211.91   $211.90   $211.90  
  Purchase #2 $113.60   8.837%   $123.6388   $123.64   $123.65   $123.60  
  Purchase #3 $67.48   3.673%   $69.9585   $69.96   $69.95   $70.00  
  Purchase #4 $246.55   8.403%   $267.2676   $267.27   $267.25   $267.30  
  Purchase #5 $68.73   4.558%   $71.8627   $71.86   $71.85   $71.90  
  Purchase #6 $14.43   7.291%   $15.4821   $15.48   $15.50   $15.50  
  Purchase #7 $239.84   8.336%   $259.8331   $259.83   $259.85   $259.80  
  7 purchase totals = $946.16       $1,019.9543   $1,019.95   $1,019.95   $1,020.00