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 $26.87   8.560%   $29.1701   $29.17   $29.15   $29.20  
  Purchase #2 $86.30   6.614%   $92.0079   $92.01   $92.00   $92.00  
  Purchase #3 $246.66   6.379%   $262.3944   $262.39   $262.40   $262.40  
  Purchase #4 $218.77   13.497%   $248.2974   $248.30   $248.30   $248.30  
  Purchase #5 $213.40   8.416%   $231.3597   $231.36   $231.35   $231.40  
  Purchase #6 $235.60   8.294%   $255.1407   $255.14   $255.15   $255.10  
  Purchase #7 $32.54   5.644%   $34.3766   $34.38   $34.40   $34.40  
  7 purchase totals = $1,060.14       $1,152.7468   $1,152.75   $1,152.75   $1,152.80