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	$72.72	7.173%	$77.9362	$77.94	$77.95	$77.90
Purchase #2	$85.96	6.449%	$91.5036	$91.50	$91.50	$91.50
Purchase #3	$90.43	11.523%	$100.8502	$100.85	$100.85	$100.90
Purchase #4	$113.71	3.628%	$117.8354	$117.84	$117.85	$117.80
Purchase #5	$91.74	4.193%	$95.5867	$95.59	$95.60	$95.60
Purchase #6	$203.56	4.366%	$212.4474	$212.45	$212.45	$212.40
Purchase #7	$113.35	8.592%	$123.089	$123.09	$123.10	$123.10
7 purchase totals =	$771.47		$819.2485	$819.26	$819.30	$819.20