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	$162.49	5.534%	$171.4822	$171.48	$171.50	$171.50
Purchase #2	$37.88	10.727%	$41.9434	$41.94	$41.95	$41.90
Purchase #3	$191.25	7.117%	$204.8613	$204.86	$204.85	$204.90
Purchase #4	$25.96	9.356%	$28.3888	$28.39	$28.40	$28.40
Purchase #5	$126.67	3.812%	$131.4987	$131.50	$131.50	$131.50
Purchase #6	$7.54	3.830%	$7.8288	$7.83	$7.85	$7.80
Purchase #7	$55.42	12.396%	$62.2899	$62.29	$62.30	$62.30
7 purchase totals =	$607.21		$648.2931	$648.29	$648.35	$648.30