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	$135.52	12.719%	$152.7568	$152.76	$152.75	$152.80
Purchase #2	$239.77	6.748%	$255.9497	$255.95	$255.95	$255.90
Purchase #3	$41.36	6.689%	$44.1266	$44.13	$44.15	$44.10
Purchase #4	$120.54	11.433%	$134.3213	$134.32	$134.30	$134.30
Purchase #5	$148.65	3.274%	$153.5168	$153.52	$153.50	$153.50
Purchase #6	$19.46	5.220%	$20.4758	$20.48	$20.50	$20.50
Purchase #7	$79.34	3.851%	$82.3954	$82.40	$82.40	$82.40
7 purchase totals =	$784.64		$843.5424	$843.56	$843.55	$843.50