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	$29.98	5.857%	$31.7359	$31.74	$31.75	$31.70
Purchase #2	$76.69	7.292%	$82.2822	$82.28	$82.30	$82.30
Purchase #3	$227.74	5.623%	$240.5458	$240.55	$240.55	$240.50
Purchase #4	$65.54	9.166%	$71.5474	$71.55	$71.55	$71.50
Purchase #5	$31.92	4.121%	$33.2354	$33.24	$33.25	$33.20
Purchase #6	$144.52	12.718%	$162.9001	$162.90	$162.90	$162.90
Purchase #7	$70.55	10.104%	$77.6784	$77.68	$77.70	$77.70
7 purchase totals =	$646.94		$699.9252	$699.94	$700.00	$699.80