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 $235.44   13.825%   $267.9896   $267.99   $268.00   $268.00  
  Purchase #2 $133.76   10.123%   $147.3005   $147.30   $147.30   $147.30  
  Purchase #3 $236.85   9.678%   $259.7723   $259.77   $259.75   $259.80  
  Purchase #4 $12.43   3.813%   $12.904   $12.90   $12.90   $12.90  
  Purchase #5 $143.54   7.273%   $153.9797   $153.98   $154.00   $154.00  
  Purchase #6 $240.65   8.411%   $260.8911   $260.89   $260.90   $260.90  
  Purchase #7 $23.38   6.542%   $24.9095   $24.91   $24.90   $24.90  
  7 purchase totals = $1,026.05       $1,127.7467   $1,127.74   $1,127.75   $1,127.80