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	$56.76	6.125%	$60.2366	$60.24	$60.25	$60.20
Purchase #2	$159.48	12.570%	$179.5266	$179.53	$179.55	$179.50
Purchase #3	$89.90	7.263%	$96.4294	$96.43	$96.45	$96.40
Purchase #4	$52.87	12.779%	$59.6263	$59.63	$59.65	$59.60
Purchase #5	$178.49	10.218%	$196.7281	$196.73	$196.75	$196.70
Purchase #6	$144.97	10.586%	$160.3165	$160.32	$160.30	$160.30
Purchase #7	$230.49	5.455%	$243.0632	$243.06	$243.05	$243.10
7 purchase totals =	$912.96		$995.9267	$995.94	$996.00	$995.80