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	$155.38	5.731%	$164.2848	$164.28	$164.30	$164.30
Purchase #2	$149.65	6.657%	$159.6122	$159.61	$159.60	$159.60
Purchase #3	$223.60	8.452%	$242.4987	$242.50	$242.50	$242.50
Purchase #4	$123.79	5.263%	$130.3051	$130.31	$130.30	$130.30
Purchase #5	$7.32	7.440%	$7.8646	$7.86	$7.85	$7.90
Purchase #6	$142.29	3.179%	$146.8134	$146.81	$146.80	$146.80
Purchase #7	$163.69	10.120%	$180.2554	$180.26	$180.25	$180.30
7 purchase totals =	$965.72		$1,031.6342	$1,031.63	$1,031.60	$1,031.70