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	$189.77	11.151%	$210.9313	$210.93	$210.95	$210.90
Purchase #2	$249.57	8.198%	$270.0297	$270.03	$270.05	$270.00
Purchase #3	$49.46	6.144%	$52.4988	$52.50	$52.50	$52.50
Purchase #4	$89.85	11.230%	$99.9402	$99.94	$99.95	$99.90
Purchase #5	$241.78	13.838%	$275.2375	$275.24	$275.25	$275.20
Purchase #6	$88.63	12.335%	$99.5625	$99.56	$99.55	$99.60
Purchase #7	$226.82	11.670%	$253.2899	$253.29	$253.30	$253.30
7 purchase totals =	$1,135.88		$1,261.4899	$1,261.49	$1,261.55	$1,261.40