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	$88.26	13.321%	$100.0171	$100.02	$100.00	$100.00
Purchase #2	$153.83	6.763%	$164.2335	$164.23	$164.25	$164.20
Purchase #3	$237.52	4.647%	$248.5576	$248.56	$248.55	$248.60
Purchase #4	$49.46	7.639%	$53.2382	$53.24	$53.25	$53.20
Purchase #5	$173.27	3.136%	$178.7037	$178.70	$178.70	$178.70
Purchase #6	$97.69	7.819%	$105.3284	$105.33	$105.35	$105.30
Purchase #7	$189.95	5.272%	$199.9642	$199.96	$199.95	$200.00
7 purchase totals =	$989.98		$1,050.0427	$1,050.04	$1,050.05	$1,050.00