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 $241.58   13.223%   $273.5241   $273.52   $273.50   $273.50  
  Purchase #2 $218.85   10.714%   $242.2976   $242.30   $242.30   $242.30  
  Purchase #3 $211.26   6.209%   $224.3771   $224.38   $224.40   $224.40  
  Purchase #4 $89.36   4.582%   $93.4545   $93.45   $93.45   $93.50  
  Purchase #5 $191.64   12.155%   $214.9338   $214.93   $214.95   $214.90  
  Purchase #6 $42.48   8.705%   $46.1779   $46.18   $46.20   $46.20  
  Purchase #7 $137.29   10.567%   $151.7974   $151.80   $151.80   $151.80  
  7 purchase totals = $1,132.46       $1,246.5624   $1,246.56   $1,246.60   $1,246.60