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	$66.75	4.132%	$69.5081	$69.51	$69.50	$69.50
Purchase #2	$149.27	7.527%	$160.5056	$160.51	$160.50	$160.50
Purchase #3	$229.66	13.498%	$260.6595	$260.66	$260.65	$260.70
Purchase #4	$18.29	10.861%	$20.2765	$20.28	$20.30	$20.30
Purchase #5	$20.75	8.433%	$22.4998	$22.50	$22.50	$22.50
Purchase #6	$225.79	13.678%	$256.6736	$256.67	$256.65	$256.70
Purchase #7	$54.69	9.550%	$59.9129	$59.91	$59.90	$59.90
7 purchase totals =	$765.20		$850.0360	$850.04	$850.00	$850.10