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 $246.82   13.151%   $279.2793   $279.28   $279.30   $279.30  
  Purchase #2 $215.32   9.474%   $235.7194   $235.72   $235.70   $235.70  
  Purchase #3 $237.77   12.540%   $267.5864   $267.59   $267.60   $267.60  
  Purchase #4 $212.43   9.694%   $233.023   $233.02   $233.00   $233.00  
  Purchase #5 $209.65   5.205%   $220.5623   $220.56   $220.55   $220.60  
  Purchase #6 $26.25   3.625%   $27.2016   $27.20   $27.20   $27.20  
  Purchase #7 $87.69   10.162%   $96.6011   $96.60   $96.60   $96.60  
  7 purchase totals = $1,235.93       $1,359.9731   $1,359.97   $1,359.95   $1,360.00