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	$244.90	10.440%	$270.4676	$270.47	$270.45	$270.50
Purchase #2	$93.87	3.424%	$97.0841	$97.08	$97.10	$97.10
Purchase #3	$53.64	3.336%	$55.4294	$55.43	$55.45	$55.40
Purchase #4	$7.98	6.117%	$8.4681	$8.47	$8.45	$8.50
Purchase #5	$85.31	6.404%	$90.7733	$90.77	$90.75	$90.80
Purchase #6	$109.73	3.514%	$113.5859	$113.59	$113.60	$113.60
Purchase #7	$168.97	5.422%	$178.1316	$178.13	$178.15	$178.10
7 purchase totals =	$764.40		$813.9400	$813.94	$813.95	$814.00