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	$28.88	7.848%	$31.1465	$31.15	$31.15	$31.10
Purchase #2	$177.42	10.533%	$196.1076	$196.11	$196.10	$196.10
Purchase #3	$211.60	4.538%	$221.2024	$221.20	$221.20	$221.20
Purchase #4	$106.28	10.652%	$117.6009	$117.60	$117.60	$117.60
Purchase #5	$109.91	13.200%	$124.4181	$124.42	$124.40	$124.40
Purchase #6	$89.81	11.773%	$100.3833	$100.38	$100.40	$100.40
Purchase #7	$201.68	12.419%	$226.7266	$226.73	$226.75	$226.70
7 purchase totals =	$925.58		$1,017.5854	$1,017.59	$1,017.60	$1,017.50