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	$67.89	8.761%	$73.8378	$73.84	$73.85	$73.80
Purchase #2	$51.89	10.399%	$57.286	$57.29	$57.30	$57.30
Purchase #3	$35.90	5.426%	$37.8479	$37.85	$37.85	$37.80
Purchase #4	$86.45	5.516%	$91.2186	$91.22	$91.20	$91.20
Purchase #5	$180.43	4.571%	$188.6775	$188.68	$188.70	$188.70
Purchase #6	$146.94	3.229%	$151.6847	$151.68	$151.70	$151.70
Purchase #7	$85.88	7.713%	$92.5039	$92.50	$92.50	$92.50
7 purchase totals =	$655.38		$693.0564	$693.06	$693.10	$693.00