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	$67.36	5.377%	$70.9819	$70.98	$71.00	$71.00
Purchase #2	$77.72	3.281%	$80.27	$80.27	$80.25	$80.30
Purchase #3	$118.41	11.148%	$131.6103	$131.61	$131.60	$131.60
Purchase #4	$156.27	6.606%	$166.5932	$166.59	$166.60	$166.60
Purchase #5	$23.95	5.773%	$25.3326	$25.33	$25.35	$25.30
Purchase #6	$138.97	9.210%	$151.7691	$151.77	$151.75	$151.80
Purchase #7	$232.85	13.592%	$264.499	$264.50	$264.50	$264.50
7 purchase totals =	$815.53		$891.0561	$891.05	$891.05	$891.10