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 $85.43   13.155%   $96.6683   $96.67   $96.65   $96.70  
  Purchase #2 $224.32   12.322%   $251.9607   $251.96   $251.95   $252.00  
  Purchase #3 $198.27   5.555%   $209.2839   $209.28   $209.30   $209.30  
  Purchase #4 $238.27   8.428%   $258.3514   $258.35   $258.35   $258.40  
  Purchase #5 $69.54   3.509%   $71.9802   $71.98   $72.00   $72.00  
  Purchase #6 $30.78   6.440%   $32.7622   $32.76   $32.75   $32.80  
  Purchase #7 $135.93   6.423%   $144.6608   $144.66   $144.65   $144.70  
  7 purchase totals = $982.54       $1,065.6675   $1,065.66   $1,065.65   $1,065.90