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	$37.64	6.627%	$40.1344	$40.13	$40.15	$40.10
Purchase #2	$196.38	12.116%	$220.1734	$220.17	$220.15	$220.20
Purchase #3	$62.78	7.204%	$67.3027	$67.30	$67.30	$67.30
Purchase #4	$195.89	8.273%	$212.096	$212.10	$212.10	$212.10
Purchase #5	$47.52	6.549%	$50.6321	$50.63	$50.65	$50.60
Purchase #6	$60.93	10.828%	$67.5275	$67.53	$67.55	$67.50
Purchase #7	$50.66	9.712%	$55.5801	$55.58	$55.60	$55.60
7 purchase totals =	$651.80		$713.4462	$713.44	$713.50	$713.40