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	$94.89	3.817%	$98.512	$98.51	$98.50	$98.50
Purchase #2	$197.67	12.802%	$222.9757	$222.98	$223.00	$223.00
Purchase #3	$180.77	7.441%	$194.2211	$194.22	$194.20	$194.20
Purchase #4	$114.94	7.443%	$123.495	$123.50	$123.50	$123.50
Purchase #5	$55.42	9.106%	$60.4665	$60.47	$60.45	$60.50
Purchase #6	$182.47	8.392%	$197.7829	$197.78	$197.80	$197.80
Purchase #7	$89.66	11.823%	$100.2605	$100.26	$100.25	$100.30
7 purchase totals =	$915.82		$997.7137	$997.72	$997.70	$997.80