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 $127.85   3.608%   $132.4628   $132.46   $132.45   $132.50  
  Purchase #2 $163.92   13.600%   $186.2131   $186.21   $186.20   $186.20  
  Purchase #3 $232.95   5.692%   $246.2095   $246.21   $246.20   $246.20  
  Purchase #4 $14.38   10.532%   $15.8945   $15.89   $15.90   $15.90  
  Purchase #5 $203.70   4.570%   $213.0091   $213.01   $213.00   $213.00  
  Purchase #6 $136.39   11.800%   $152.484   $152.48   $152.50   $152.50  
  Purchase #7 $151.98   10.543%   $168.0033   $168.00   $168.00   $168.00  
  7 purchase totals = $1,031.17       $1,114.2763   $1,114.26   $1,114.25   $1,114.30