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	$96.95	3.539%	$100.3811	$100.38	$100.40	$100.40
Purchase #2	$96.39	6.833%	$102.9763	$102.98	$103.00	$103.00
Purchase #3	$144.55	9.400%	$158.1377	$158.14	$158.15	$158.10
Purchase #4	$165.27	6.120%	$175.3845	$175.38	$175.40	$175.40
Purchase #5	$91.88	8.606%	$99.7872	$99.79	$99.80	$99.80
Purchase #6	$52.77	3.596%	$54.6676	$54.67	$54.65	$54.70
Purchase #7	$8.25	7.199%	$8.8439	$8.84	$8.85	$8.80
7 purchase totals =	$656.06		$700.1783	$700.18	$700.25	$700.20