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	$65.47	12.868%	$73.8947	$73.89	$73.90	$73.90
Purchase #2	$247.33	4.131%	$257.5472	$257.55	$257.55	$257.50
Purchase #3	$33.97	13.225%	$38.4625	$38.46	$38.45	$38.50
Purchase #4	$222.86	9.743%	$244.5732	$244.57	$244.55	$244.60
Purchase #5	$120.52	11.442%	$134.3099	$134.31	$134.30	$134.30
Purchase #6	$232.72	13.670%	$264.5328	$264.53	$264.55	$264.50
Purchase #7	$67.60	12.209%	$75.8533	$75.85	$75.85	$75.90
7 purchase totals =	$990.47		$1,089.1736	$1,089.16	$1,089.15	$1,089.20