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 $96.93   13.116%   $109.6433   $109.64   $109.65   $109.60  
  Purchase #2 $163.60   3.722%   $169.6892   $169.69   $169.70   $169.70  
  Purchase #3 $246.68   11.758%   $275.6846   $275.68   $275.70   $275.70  
  Purchase #4 $105.27   11.370%   $117.2392   $117.24   $117.25   $117.20  
  Purchase #5 $163.29   5.714%   $172.6204   $172.62   $172.60   $172.60  
  Purchase #6 $53.91   8.253%   $58.3592   $58.36   $58.35   $58.40  
  Purchase #7 $141.25   4.263%   $147.2715   $147.27   $147.25   $147.30  
  7 purchase totals = $970.93       $1,050.5074   $1,050.50   $1,050.50   $1,050.50