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	$20.95	4.428%	$21.8777	$21.88	$21.90	$21.90
Purchase #2	$89.44	11.537%	$99.7587	$99.76	$99.75	$99.80
Purchase #3	$215.96	13.204%	$244.4754	$244.48	$244.50	$244.50
Purchase #4	$166.56	5.461%	$175.6558	$175.66	$175.65	$175.70
Purchase #5	$41.59	10.812%	$46.0867	$46.09	$46.10	$46.10
Purchase #6	$143.36	3.615%	$148.5425	$148.54	$148.55	$148.50
Purchase #7	$52.84	6.134%	$56.0812	$56.08	$56.10	$56.10
7 purchase totals =	$730.70		$792.4780	$792.49	$792.55	$792.60