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	$63.87	11.613%	$71.2872	$71.29	$71.30	$71.30
Purchase #2	$37.59	10.665%	$41.599	$41.60	$41.60	$41.60
Purchase #3	$59.89	4.471%	$62.5677	$62.57	$62.55	$62.60
Purchase #4	$101.98	12.830%	$115.064	$115.06	$115.05	$115.10
Purchase #5	$235.66	12.107%	$264.1914	$264.19	$264.20	$264.20
Purchase #6	$72.85	9.625%	$79.8618	$79.86	$79.85	$79.90
Purchase #7	$157.71	13.401%	$178.8447	$178.84	$178.85	$178.80
7 purchase totals =	$729.55		$813.4158	$813.41	$813.40	$813.50