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 $246.52   6.383%   $262.2554   $262.26   $262.25   $262.30  
  Purchase #2 $190.85   3.561%   $197.6462   $197.65   $197.65   $197.60  
  Purchase #3 $113.36   8.736%   $123.2631   $123.26   $123.25   $123.30  
  Purchase #4 $213.46   3.157%   $220.1989   $220.20   $220.20   $220.20  
  Purchase #5 $168.74   9.737%   $185.1702   $185.17   $185.15   $185.20  
  Purchase #6 $35.83   7.498%   $38.5165   $38.52   $38.50   $38.50  
  Purchase #7 $16.66   9.858%   $18.3023   $18.30   $18.30   $18.30  
  7 purchase totals = $985.42       $1,045.3526   $1,045.36   $1,045.30   $1,045.40