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	$49.96	13.536%	$56.7226	$56.72	$56.70	$56.70
Purchase #2	$250.82	6.354%	$266.7571	$266.76	$266.75	$266.80
Purchase #3	$79.78	5.577%	$84.2293	$84.23	$84.25	$84.20
Purchase #4	$36.52	3.794%	$37.9056	$37.91	$37.90	$37.90
Purchase #5	$51.44	4.717%	$53.8664	$53.87	$53.85	$53.90
Purchase #6	$180.38	4.542%	$188.5729	$188.57	$188.55	$188.60
Purchase #7	$103.82	4.571%	$108.5656	$108.57	$108.55	$108.60
7 purchase totals =	$752.72		$796.6195	$796.63	$796.55	$796.70