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	$9.76	6.868%	$10.4303	$10.43	$10.45	$10.40
Purchase #2	$111.40	10.796%	$123.4267	$123.43	$123.45	$123.40
Purchase #3	$140.96	9.308%	$154.0806	$154.08	$154.10	$154.10
Purchase #4	$131.60	6.557%	$140.229	$140.23	$140.25	$140.20
Purchase #5	$61.78	4.505%	$64.5632	$64.56	$64.55	$64.60
Purchase #6	$194.88	10.467%	$215.2781	$215.28	$215.30	$215.30
Purchase #7	$168.44	10.399%	$185.9561	$185.96	$185.95	$186.00
7 purchase totals =	$818.82		$893.9640	$893.97	$894.05	$894.00