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	$175.74	13.438%	$199.3559	$199.36	$199.35	$199.40
Purchase #2	$217.70	12.333%	$244.5489	$244.55	$244.55	$244.50
Purchase #3	$240.76	9.297%	$263.1435	$263.14	$263.15	$263.10
Purchase #4	$222.47	10.810%	$246.519	$246.52	$246.50	$246.50
Purchase #5	$59.74	11.790%	$66.7833	$66.78	$66.80	$66.80
Purchase #6	$92.97	12.520%	$104.6098	$104.61	$104.60	$104.60
Purchase #7	$24.94	3.751%	$25.8755	$25.88	$25.90	$25.90
7 purchase totals =	$1,034.32		$1,150.8359	$1,150.84	$1,150.85	$1,150.80