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	$209.71	10.144%	$230.983	$230.98	$231.00	$231.00
Purchase #2	$184.78	6.564%	$196.909	$196.91	$196.90	$196.90
Purchase #3	$42.29	5.836%	$44.758	$44.76	$44.75	$44.80
Purchase #4	$47.77	6.104%	$50.6859	$50.69	$50.70	$50.70
Purchase #5	$49.89	7.483%	$53.6233	$53.62	$53.60	$53.60
Purchase #6	$55.94	6.542%	$59.5996	$59.60	$59.60	$59.60
Purchase #7	$34.74	7.688%	$37.4108	$37.41	$37.40	$37.40
7 purchase totals =	$625.12		$673.9696	$673.97	$673.95	$674.00