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	$117.41	4.476%	$122.6653	$122.67	$122.65	$122.70
Purchase #2	$230.92	12.829%	$260.5447	$260.54	$260.55	$260.50
Purchase #3	$94.59	10.643%	$104.6572	$104.66	$104.65	$104.70
Purchase #4	$91.39	4.474%	$95.4788	$95.48	$95.50	$95.50
Purchase #5	$110.54	12.508%	$124.3663	$124.37	$124.35	$124.40
Purchase #6	$85.64	5.287%	$90.1678	$90.17	$90.15	$90.20
Purchase #7	$209.33	13.813%	$238.2448	$238.24	$238.25	$238.20
7 purchase totals =	$939.82		$1,036.1249	$1,036.13	$1,036.10	$1,036.20