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	$99.39	12.145%	$111.4609	$111.46	$111.45	$111.50
Purchase #2	$130.85	12.696%	$147.4627	$147.46	$147.45	$147.50
Purchase #3	$210.76	4.859%	$221.0008	$221.00	$221.00	$221.00
Purchase #4	$135.26	9.586%	$148.226	$148.23	$148.25	$148.20
Purchase #5	$190.57	3.640%	$197.5067	$197.51	$197.50	$197.50
Purchase #6	$151.47	11.441%	$168.7997	$168.80	$168.80	$168.80
Purchase #7	$122.46	7.482%	$131.6225	$131.62	$131.60	$131.60
7 purchase totals =	$1,040.76		$1,126.0793	$1,126.08	$1,126.05	$1,126.10