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	$42.72	8.790%	$46.4751	$46.48	$46.50	$46.50
Purchase #2	$222.30	11.458%	$247.7711	$247.77	$247.75	$247.80
Purchase #3	$178.62	12.233%	$200.4706	$200.47	$200.45	$200.50
Purchase #4	$71.41	13.591%	$81.1153	$81.12	$81.10	$81.10
Purchase #5	$92.59	8.463%	$100.4259	$100.43	$100.45	$100.40
Purchase #6	$221.72	4.435%	$231.5533	$231.55	$231.55	$231.60
Purchase #7	$199.92	11.608%	$223.1267	$223.13	$223.15	$223.10
7 purchase totals =	$1,029.28		$1,130.9380	$1,130.95	$1,130.95	$1,131.00