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	$104.68	8.392%	$113.4647	$113.46	$113.45	$113.50
Purchase #2	$62.66	8.397%	$67.9216	$67.92	$67.90	$67.90
Purchase #3	$241.27	10.175%	$265.8192	$265.82	$265.80	$265.80
Purchase #4	$42.41	6.718%	$45.2591	$45.26	$45.25	$45.30
Purchase #5	$61.89	7.408%	$66.4748	$66.47	$66.45	$66.50
Purchase #6	$213.56	4.480%	$223.1275	$223.13	$223.15	$223.10
Purchase #7	$37.30	6.782%	$39.8297	$39.83	$39.85	$39.80
7 purchase totals =	$763.77		$821.8966	$821.89	$821.85	$821.90