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	$210.54	6.354%	$223.9177	$223.92	$223.90	$223.90
Purchase #2	$59.28	3.743%	$61.4989	$61.50	$61.50	$61.50
Purchase #3	$19.38	7.867%	$20.9046	$20.90	$20.90	$20.90
Purchase #4	$103.79	11.192%	$115.4062	$115.41	$115.40	$115.40
Purchase #5	$95.40	4.386%	$99.5842	$99.58	$99.60	$99.60
Purchase #6	$125.33	10.479%	$138.4633	$138.46	$138.45	$138.50
Purchase #7	$144.26	13.483%	$163.7106	$163.71	$163.70	$163.70
7 purchase totals =	$757.98		$823.4855	$823.48	$823.45	$823.50