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 $186.53   9.230%   $203.7467   $203.75   $203.75   $203.70  
  Purchase #2 $185.44   9.777%   $203.5705   $203.57   $203.55   $203.60  
  Purchase #3 $246.91   10.649%   $273.2034   $273.20   $273.20   $273.20  
  Purchase #4 $59.46   11.525%   $66.3128   $66.31   $66.30   $66.30  
  Purchase #5 $208.25   11.471%   $232.1384   $232.14   $232.15   $232.10  
  Purchase #6 $227.81   9.267%   $248.9212   $248.92   $248.90   $248.90  
  Purchase #7 $111.91   5.422%   $117.9778   $117.98   $118.00   $118.00  
  7 purchase totals = $1,226.31       $1,345.8708   $1,345.87   $1,345.85   $1,345.80