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	$6.45	10.435%	$7.1231	$7.12	$7.10	$7.10
Purchase #2	$220.74	13.580%	$250.7165	$250.72	$250.70	$250.70
Purchase #3	$42.67	6.637%	$45.502	$45.50	$45.50	$45.50
Purchase #4	$239.96	6.227%	$254.9023	$254.90	$254.90	$254.90
Purchase #5	$102.96	8.624%	$111.8393	$111.84	$111.85	$111.80
Purchase #6	$57.40	5.170%	$60.3676	$60.37	$60.35	$60.40
Purchase #7	$159.36	5.340%	$167.8698	$167.87	$167.85	$167.90
7 purchase totals =	$829.54		$898.3206	$898.32	$898.25	$898.30