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	$156.42	6.222%	$166.1525	$166.15	$166.15	$166.20
Purchase #2	$56.33	7.473%	$60.5395	$60.54	$60.55	$60.50
Purchase #3	$149.80	10.490%	$165.514	$165.51	$165.50	$165.50
Purchase #4	$161.36	12.695%	$181.8447	$181.84	$181.85	$181.80
Purchase #5	$210.87	5.570%	$222.6155	$222.62	$222.60	$222.60
Purchase #6	$102.70	6.284%	$109.1537	$109.15	$109.15	$109.20
Purchase #7	$167.49	11.807%	$187.2655	$187.27	$187.25	$187.30
7 purchase totals =	$1,004.97		$1,093.0854	$1,093.08	$1,093.05	$1,093.10