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 $48.47   8.371%   $52.5274   $52.53   $52.55   $52.50  
  Purchase #2 $239.97   7.565%   $258.1237   $258.12   $258.10   $258.10  
  Purchase #3 $103.79   3.579%   $107.5046   $107.50   $107.50   $107.50  
  Purchase #4 $59.36   10.666%   $65.6913   $65.69   $65.70   $65.70  
  Purchase #5 $154.91   7.584%   $166.6584   $166.66   $166.65   $166.70  
  Purchase #6 $191.74   11.403%   $213.6041   $213.60   $213.60   $213.60  
  Purchase #7 $235.72   12.866%   $266.0477   $266.05   $266.05   $266.00  
  7 purchase totals = $1,033.96       $1,130.1572   $1,130.15   $1,130.15   $1,130.10