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 $243.61   8.772%   $264.9795   $264.98   $265.00   $265.00  
  Purchase #2 $81.46   13.435%   $92.4042   $92.40   $92.40   $92.40  
  Purchase #3 $144.88   11.337%   $161.305   $161.31   $161.30   $161.30  
  Purchase #4 $227.74   7.420%   $244.6383   $244.64   $244.65   $244.60  
  Purchase #5 $220.29   3.122%   $227.1675   $227.17   $227.15   $227.20  
  Purchase #6 $160.95   4.737%   $168.5742   $168.57   $168.55   $168.60  
  Purchase #7 $70.63   10.814%   $78.2679   $78.27   $78.25   $78.30  
  7 purchase totals = $1,149.56       $1,237.3366   $1,237.34   $1,237.30   $1,237.40