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	$53.89	4.795%	$56.474	$56.47	$56.45	$56.50
Purchase #2	$208.86	3.342%	$215.8401	$215.84	$215.85	$215.80
Purchase #3	$99.33	5.303%	$104.5975	$104.60	$104.60	$104.60
Purchase #4	$76.93	4.140%	$80.1149	$80.11	$80.10	$80.10
Purchase #5	$23.47	8.566%	$25.4804	$25.48	$25.50	$25.50
Purchase #6	$158.28	10.409%	$174.7554	$174.76	$174.75	$174.80
Purchase #7	$30.76	3.720%	$31.9043	$31.90	$31.90	$31.90
7 purchase totals =	$651.52		$689.1666	$689.16	$689.15	$689.20