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	$79.68	4.579%	$83.3285	$83.33	$83.35	$83.30
Purchase #2	$156.52	5.512%	$165.1474	$165.15	$165.15	$165.10
Purchase #3	$140.51	10.605%	$155.4111	$155.41	$155.40	$155.40
Purchase #4	$56.48	9.135%	$61.6394	$61.64	$61.65	$61.60
Purchase #5	$164.64	13.338%	$186.5997	$186.60	$186.60	$186.60
Purchase #6	$89.72	5.512%	$94.6654	$94.67	$94.65	$94.70
Purchase #7	$65.53	3.102%	$67.5627	$67.56	$67.55	$67.60
7 purchase totals =	$753.08		$814.3542	$814.36	$814.35	$814.30