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 $207.91   3.771%   $215.7503   $215.75   $215.75   $215.80  
  Purchase #2 $67.70   11.236%   $75.3068   $75.31   $75.30   $75.30  
  Purchase #3 $139.26   5.509%   $146.9318   $146.93   $146.95   $146.90  
  Purchase #4 $242.63   11.182%   $269.7609   $269.76   $269.75   $269.80  
  Purchase #5 $126.57   3.485%   $130.981   $130.98   $131.00   $131.00  
  Purchase #6 $120.83   4.747%   $126.5658   $126.57   $126.55   $126.60  
  Purchase #7 $205.74   5.280%   $216.6031   $216.60   $216.60   $216.60  
  7 purchase totals = $1,110.64       $1,181.8997   $1,181.90   $1,181.90   $1,182.00