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 $59.81   9.118%   $65.2635   $65.26   $65.25   $65.30  
  Purchase #2 $68.58   8.697%   $74.5444   $74.54   $74.55   $74.50  
  Purchase #3 $159.94   5.298%   $168.4136   $168.41   $168.40   $168.40  
  Purchase #4 $220.59   4.496%   $230.5077   $230.51   $230.50   $230.50  
  Purchase #5 $240.75   9.106%   $262.6727   $262.67   $262.65   $262.70  
  Purchase #6 $192.34   10.129%   $211.8221   $211.82   $211.80   $211.80  
  Purchase #7 $10.86   3.242%   $11.2121   $11.21   $11.20   $11.20  
  7 purchase totals = $952.87       $1,024.4361   $1,024.42   $1,024.35   $1,024.40