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	$37.42	6.506%	$39.8545	$39.85	$39.85	$39.90
Purchase #2	$237.25	5.433%	$250.1398	$250.14	$250.15	$250.10
Purchase #3	$156.83	4.690%	$164.1853	$164.19	$164.20	$164.20
Purchase #4	$244.77	7.556%	$263.2648	$263.26	$263.25	$263.30
Purchase #5	$171.32	5.499%	$180.7409	$180.74	$180.75	$180.70
Purchase #6	$177.59	10.509%	$196.2529	$196.25	$196.25	$196.30
Purchase #7	$42.50	7.174%	$45.549	$45.55	$45.55	$45.50
7 purchase totals =	$1,067.68		$1,139.9872	$1,139.98	$1,140.00	$1,140.00