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 $218.48   13.510%   $247.9966   $248.00   $248.00   $248.00  
  Purchase #2 $203.83   4.499%   $213.0003   $213.00   $213.00   $213.00  
  Purchase #3 $83.32   8.726%   $90.5905   $90.59   $90.60   $90.60  
  Purchase #4 $45.57   6.844%   $48.6888   $48.69   $48.70   $48.70  
  Purchase #5 $176.84   13.518%   $200.7452   $200.75   $200.75   $200.70  
  Purchase #6 $235.83   11.370%   $262.6439   $262.64   $262.65   $262.60  
  Purchase #7 $228.82   13.363%   $259.3972   $259.40   $259.40   $259.40  
  7 purchase totals = $1,192.69       $1,323.0625   $1,323.07   $1,323.10   $1,323.00