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 $235.33   10.499%   $260.0373   $260.04   $260.05   $260.00  
  Purchase #2 $176.95   12.239%   $198.6069   $198.61   $198.60   $198.60  
  Purchase #3 $54.36   13.474%   $61.6845   $61.68   $61.70   $61.70  
  Purchase #4 $114.89   5.498%   $121.2067   $121.21   $121.20   $121.20  
  Purchase #5 $129.84   5.338%   $136.7709   $136.77   $136.75   $136.80  
  Purchase #6 $186.34   6.818%   $199.0447   $199.04   $199.05   $199.00  
  Purchase #7 $144.99   7.141%   $155.3437   $155.34   $155.35   $155.30  
  7 purchase totals = $1,042.70       $1,132.6947   $1,132.69   $1,132.70   $1,132.60