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 $248.66   10.165%   $273.9363   $273.94   $273.95   $273.90  
  Purchase #2 $168.45   8.595%   $182.9283   $182.93   $182.95   $182.90  
  Purchase #3 $59.88   10.151%   $65.9584   $65.96   $65.95   $66.00  
  Purchase #4 $126.45   13.663%   $143.7269   $143.73   $143.75   $143.70  
  Purchase #5 $185.33   9.789%   $203.472   $203.47   $203.45   $203.50  
  Purchase #6 $176.57   9.784%   $193.8456   $193.85   $193.85   $193.80  
  Purchase #7 $153.41   6.513%   $163.4016   $163.40   $163.40   $163.40  
  7 purchase totals = $1,118.75       $1,227.2691   $1,227.28   $1,227.30   $1,227.20