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 $244.63   8.452%   $265.3061   $265.31   $265.30   $265.30  
  Purchase #2 $209.69   6.663%   $223.6616   $223.66   $223.65   $223.70  
  Purchase #3 $242.27   7.220%   $259.7619   $259.76   $259.75   $259.80  
  Purchase #4 $56.78   5.546%   $59.929   $59.93   $59.95   $59.90  
  Purchase #5 $130.59   8.785%   $142.0623   $142.06   $142.05   $142.10  
  Purchase #6 $107.68   11.774%   $120.3582   $120.36   $120.35   $120.40  
  Purchase #7 $248.99   6.432%   $265.005   $265.01   $265.00   $265.00  
  7 purchase totals = $1,240.63       $1,336.0841   $1,336.09   $1,336.05   $1,336.20