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	$26.87	3.317%	$27.7613	$27.76	$27.75	$27.80
Purchase #2	$82.90	11.612%	$92.5263	$92.53	$92.55	$92.50
Purchase #3	$198.95	3.238%	$205.392	$205.39	$205.40	$205.40
Purchase #4	$178.32	7.159%	$191.0859	$191.09	$191.10	$191.10
Purchase #5	$93.64	6.231%	$99.4747	$99.47	$99.45	$99.50
Purchase #6	$134.80	12.712%	$151.9358	$151.94	$151.95	$151.90
Purchase #7	$216.38	10.434%	$238.9571	$238.96	$238.95	$239.00
7 purchase totals =	$931.86		$1,007.1331	$1,007.14	$1,007.15	$1,007.20