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	$30.69	8.428%	$33.2766	$33.28	$33.30	$33.30
Purchase #2	$81.41	10.121%	$89.6495	$89.65	$89.65	$89.60
Purchase #3	$92.99	4.861%	$97.5102	$97.51	$97.50	$97.50
Purchase #4	$106.44	13.196%	$120.4858	$120.49	$120.50	$120.50
Purchase #5	$150.66	5.392%	$158.7836	$158.78	$158.80	$158.80
Purchase #6	$228.43	13.454%	$259.163	$259.16	$259.15	$259.20
Purchase #7	$117.27	12.352%	$131.7552	$131.76	$131.75	$131.80
7 purchase totals =	$807.89		$890.6239	$890.63	$890.65	$890.70