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	$42.34	3.708%	$43.91	$43.91	$43.90	$43.90
Purchase #2	$242.36	13.639%	$275.4155	$275.42	$275.40	$275.40
Purchase #3	$37.55	10.347%	$41.4353	$41.44	$41.45	$41.40
Purchase #4	$188.76	3.865%	$196.0556	$196.06	$196.05	$196.10
Purchase #5	$28.96	12.388%	$32.5476	$32.55	$32.55	$32.50
Purchase #6	$70.48	7.576%	$75.8196	$75.82	$75.80	$75.80
Purchase #7	$43.27	12.252%	$48.5714	$48.57	$48.55	$48.60
7 purchase totals =	$653.72		$713.7550	$713.77	$713.70	$713.70