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	$142.62	13.290%	$161.5742	$161.57	$161.55	$161.60
Purchase #2	$228.45	12.241%	$256.4146	$256.41	$256.40	$256.40
Purchase #3	$100.41	11.560%	$112.0174	$112.02	$112.00	$112.00
Purchase #4	$80.25	11.373%	$89.3768	$89.38	$89.40	$89.40
Purchase #5	$103.36	13.439%	$117.2506	$117.25	$117.25	$117.30
Purchase #6	$70.43	12.580%	$79.2901	$79.29	$79.30	$79.30
Purchase #7	$53.51	4.428%	$55.8794	$55.88	$55.90	$55.90
7 purchase totals =	$779.03		$871.8031	$871.80	$871.80	$871.90