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 $135.59   6.602%   $144.5417   $144.54   $144.55   $144.50  
  Purchase #2 $106.41   10.270%   $117.3383   $117.34   $117.35   $117.30  
  Purchase #3 $193.72   12.254%   $217.4584   $217.46   $217.45   $217.50  
  Purchase #4 $245.88   4.623%   $257.247   $257.25   $257.25   $257.20  
  Purchase #5 $64.90   3.239%   $67.0021   $67.00   $67.00   $67.00  
  Purchase #6 $195.36   10.544%   $215.9588   $215.96   $215.95   $216.00  
  Purchase #7 $33.65   10.445%   $37.1647   $37.16   $37.15   $37.20  
  7 purchase totals = $975.51       $1,056.7110   $1,056.71   $1,056.70   $1,056.70