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	$122.83	6.734%	$131.1014	$131.10	$131.10	$131.10
Purchase #2	$52.66	7.428%	$56.5716	$56.57	$56.55	$56.60
Purchase #3	$180.86	13.570%	$205.4027	$205.40	$205.40	$205.40
Purchase #4	$82.69	7.342%	$88.7611	$88.76	$88.75	$88.80
Purchase #5	$153.95	5.375%	$162.2248	$162.22	$162.20	$162.20
Purchase #6	$82.84	7.828%	$89.3247	$89.32	$89.30	$89.30
Purchase #7	$140.82	8.131%	$152.2701	$152.27	$152.25	$152.30
7 purchase totals =	$816.65		$885.6564	$885.64	$885.55	$885.70