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	$237.30	12.476%	$266.9055	$266.91	$266.90	$266.90
Purchase #2	$214.36	8.749%	$233.1144	$233.11	$233.10	$233.10
Purchase #3	$63.76	12.683%	$71.8467	$71.85	$71.85	$71.80
Purchase #4	$159.96	5.699%	$169.0761	$169.08	$169.10	$169.10
Purchase #5	$129.33	9.620%	$141.7715	$141.77	$141.75	$141.80
Purchase #6	$88.38	9.560%	$96.8291	$96.83	$96.85	$96.80
Purchase #7	$119.52	6.516%	$127.3079	$127.31	$127.30	$127.30
7 purchase totals =	$1,012.61		$1,106.8512	$1,106.86	$1,106.85	$1,106.80