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	$20.33	5.478%	$21.4437	$21.44	$21.45	$21.40
Purchase #2	$51.63	6.488%	$54.9798	$54.98	$55.00	$55.00
Purchase #3	$194.76	5.229%	$204.944	$204.94	$204.95	$204.90
Purchase #4	$173.55	10.234%	$191.3111	$191.31	$191.30	$191.30
Purchase #5	$249.28	7.745%	$268.5867	$268.59	$268.60	$268.60
Purchase #6	$146.76	5.814%	$155.2926	$155.29	$155.30	$155.30
Purchase #7	$37.41	6.287%	$39.762	$39.76	$39.75	$39.80
7 purchase totals =	$873.72		$936.3199	$936.31	$936.35	$936.30