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 $45.50   4.551%   $47.5707   $47.57   $47.55   $47.60  
  Purchase #2 $233.81   4.211%   $243.6557   $243.66   $243.65   $243.70  
  Purchase #3 $227.89   11.134%   $253.2633   $253.26   $253.25   $253.30  
  Purchase #4 $237.28   11.688%   $265.0133   $265.01   $265.00   $265.00  
  Purchase #5 $157.33   10.326%   $173.5759   $173.58   $173.60   $173.60  
  Purchase #6 $56.28   6.856%   $60.1386   $60.14   $60.15   $60.10  
  Purchase #7 $217.74   4.581%   $227.7147   $227.71   $227.70   $227.70  
  7 purchase totals = $1,175.83       $1,270.9322   $1,270.93   $1,270.90   $1,271.00