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	$160.31	6.798%	$171.2079	$171.21	$171.20	$171.20
Purchase #2	$228.37	8.281%	$247.2813	$247.28	$247.30	$247.30
Purchase #3	$179.91	9.162%	$196.3934	$196.39	$196.40	$196.40
Purchase #4	$145.67	11.553%	$162.4993	$162.50	$162.50	$162.50
Purchase #5	$79.46	12.344%	$89.2685	$89.27	$89.25	$89.30
Purchase #6	$167.29	7.170%	$179.2847	$179.28	$179.30	$179.30
Purchase #7	$190.55	10.782%	$211.0951	$211.10	$211.10	$211.10
7 purchase totals =	$1,151.56		$1,257.0302	$1,257.03	$1,257.05	$1,257.10