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	$46.66	11.211%	$51.8911	$51.89	$51.90	$51.90
Purchase #2	$247.62	4.709%	$259.2804	$259.28	$259.30	$259.30
Purchase #3	$123.96	10.777%	$137.3192	$137.32	$137.30	$137.30
Purchase #4	$118.92	7.867%	$128.2754	$128.28	$128.30	$128.30
Purchase #5	$42.69	11.409%	$47.5605	$47.56	$47.55	$47.60
Purchase #6	$31.39	4.689%	$32.8619	$32.86	$32.85	$32.90
Purchase #7	$158.55	10.842%	$175.74	$175.74	$175.75	$175.70
7 purchase totals =	$769.79		$832.9285	$832.93	$832.95	$833.00