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	$229.46	12.872%	$258.9961	$259.00	$259.00	$259.00
Purchase #2	$120.28	8.158%	$130.0924	$130.09	$130.10	$130.10
Purchase #3	$103.57	12.860%	$116.8891	$116.89	$116.90	$116.90
Purchase #4	$82.85	11.844%	$92.6628	$92.66	$92.65	$92.70
Purchase #5	$80.87	10.113%	$89.0484	$89.05	$89.05	$89.00
Purchase #6	$128.37	3.529%	$132.9002	$132.90	$132.90	$132.90
Purchase #7	$47.85	5.229%	$50.3521	$50.35	$50.35	$50.40
7 purchase totals =	$793.25		$870.9411	$870.94	$870.95	$871.00