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 $246.95   8.466%   $267.8568   $267.86   $267.85   $267.90  
  Purchase #2 $238.74   5.570%   $252.0378   $252.04   $252.05   $252.00  
  Purchase #3 $35.30   5.565%   $37.2644   $37.26   $37.25   $37.30  
  Purchase #4 $71.95   7.595%   $77.4146   $77.41   $77.40   $77.40  
  Purchase #5 $101.90   11.183%   $113.2955   $113.30   $113.30   $113.30  
  Purchase #6 $240.93   10.230%   $265.5771   $265.58   $265.60   $265.60  
  Purchase #7 $238.62   10.371%   $263.3673   $263.37   $263.35   $263.40  
  7 purchase totals = $1,174.39       $1,276.8135   $1,276.82   $1,276.80   $1,276.90