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	$46.32	9.656%	$50.7927	$50.79	$50.80	$50.80
Purchase #2	$164.41	4.504%	$171.815	$171.82	$171.80	$171.80
Purchase #3	$84.64	13.798%	$96.3186	$96.32	$96.30	$96.30
Purchase #4	$18.70	11.579%	$20.8653	$20.87	$20.85	$20.90
Purchase #5	$179.89	9.469%	$196.9238	$196.92	$196.90	$196.90
Purchase #6	$248.77	11.504%	$277.3885	$277.39	$277.40	$277.40
Purchase #7	$71.89	10.239%	$79.2508	$79.25	$79.25	$79.30
7 purchase totals =	$814.62		$893.3547	$893.36	$893.30	$893.40