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	$92.75	6.720%	$98.9828	$98.98	$99.00	$99.00
Purchase #2	$103.27	8.135%	$111.671	$111.67	$111.65	$111.70
Purchase #3	$61.79	5.698%	$65.3108	$65.31	$65.30	$65.30
Purchase #4	$39.52	12.775%	$44.5687	$44.57	$44.55	$44.60
Purchase #5	$48.62	10.382%	$53.6677	$53.67	$53.65	$53.70
Purchase #6	$140.52	4.270%	$146.5202	$146.52	$146.50	$146.50
Purchase #7	$85.59	6.862%	$91.4632	$91.46	$91.45	$91.50
7 purchase totals =	$572.06		$612.1844	$612.18	$612.10	$612.30