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	$170.58	4.365%	$178.0258	$178.03	$178.05	$178.00
Purchase #2	$200.83	7.846%	$216.5871	$216.59	$216.60	$216.60
Purchase #3	$148.33	11.828%	$165.8745	$165.87	$165.85	$165.90
Purchase #4	$222.32	11.659%	$248.2403	$248.24	$248.25	$248.20
Purchase #5	$146.83	6.347%	$156.1493	$156.15	$156.15	$156.10
Purchase #6	$174.54	11.678%	$194.9228	$194.92	$194.90	$194.90
Purchase #7	$209.63	9.728%	$230.0228	$230.02	$230.00	$230.00
7 purchase totals =	$1,273.06		$1,389.8226	$1,389.82	$1,389.80	$1,389.70