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	$212.41	13.103%	$240.2421	$240.24	$240.25	$240.20
Purchase #2	$68.97	8.269%	$74.6731	$74.67	$74.65	$74.70
Purchase #3	$122.61	7.473%	$131.7726	$131.77	$131.75	$131.80
Purchase #4	$222.43	7.368%	$238.8186	$238.82	$238.80	$238.80
Purchase #5	$201.42	5.223%	$211.9402	$211.94	$211.95	$211.90
Purchase #6	$72.50	12.362%	$81.4625	$81.46	$81.45	$81.50
Purchase #7	$44.59	4.274%	$46.4958	$46.50	$46.50	$46.50
7 purchase totals =	$944.93		$1,025.4049	$1,025.40	$1,025.35	$1,025.40