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 $245.79   8.492%   $266.6625   $266.66   $266.65   $266.70  
  Purchase #2 $105.45   9.382%   $115.3433   $115.34   $115.35   $115.30  
  Purchase #3 $243.52   3.580%   $252.238   $252.24   $252.25   $252.20  
  Purchase #4 $224.36   4.688%   $234.878   $234.88   $234.90   $234.90  
  Purchase #5 $85.75   12.759%   $96.6908   $96.69   $96.70   $96.70  
  Purchase #6 $36.92   7.119%   $39.5483   $39.55   $39.55   $39.50  
  Purchase #7 $248.61   13.497%   $282.1649   $282.16   $282.15   $282.20  
  7 purchase totals = $1,190.40       $1,287.5258   $1,287.52   $1,287.55   $1,287.50