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	$130.32	7.119%	$139.5975	$139.60	$139.60	$139.60
Purchase #2	$235.74	10.241%	$259.8821	$259.88	$259.90	$259.90
Purchase #3	$233.41	9.111%	$254.676	$254.68	$254.70	$254.70
Purchase #4	$148.93	6.428%	$158.5032	$158.50	$158.50	$158.50
Purchase #5	$149.95	12.187%	$168.2244	$168.22	$168.20	$168.20
Purchase #6	$69.30	12.514%	$77.9722	$77.97	$77.95	$78.00
Purchase #7	$182.27	7.641%	$196.1973	$196.20	$196.20	$196.20
7 purchase totals =	$1,149.92		$1,255.0527	$1,255.05	$1,255.05	$1,255.10