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	$77.78	13.666%	$88.4094	$88.41	$88.40	$88.40
Purchase #2	$139.73	6.283%	$148.5092	$148.51	$148.50	$148.50
Purchase #3	$195.53	7.704%	$210.5936	$210.59	$210.60	$210.60
Purchase #4	$166.38	9.328%	$181.8999	$181.90	$181.90	$181.90
Purchase #5	$99.43	11.732%	$111.0951	$111.10	$111.10	$111.10
Purchase #6	$68.58	13.339%	$77.7279	$77.73	$77.75	$77.70
Purchase #7	$161.82	9.104%	$176.5521	$176.55	$176.55	$176.60
7 purchase totals =	$909.25		$994.7872	$994.79	$994.80	$994.80