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	$11.84	12.595%	$13.3312	$13.33	$13.35	$13.30
Purchase #2	$242.88	11.783%	$271.4986	$271.50	$271.50	$271.50
Purchase #3	$137.37	11.210%	$152.7692	$152.77	$152.75	$152.80
Purchase #4	$195.48	4.501%	$204.2786	$204.28	$204.30	$204.30
Purchase #5	$26.38	3.415%	$27.2809	$27.28	$27.30	$27.30
Purchase #6	$103.43	8.178%	$111.8885	$111.89	$111.90	$111.90
Purchase #7	$44.53	6.183%	$47.2833	$47.28	$47.30	$47.30
7 purchase totals =	$761.91		$828.3303	$828.33	$828.40	$828.40