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	$32.54	11.486%	$36.2775	$36.28	$36.30	$36.30
Purchase #2	$123.96	3.109%	$127.8139	$127.81	$127.80	$127.80
Purchase #3	$127.25	10.355%	$140.4267	$140.43	$140.45	$140.40
Purchase #4	$191.49	10.714%	$212.0062	$212.01	$212.00	$212.00
Purchase #5	$39.29	9.205%	$42.9066	$42.91	$42.90	$42.90
Purchase #6	$178.93	10.818%	$198.2866	$198.29	$198.30	$198.30
Purchase #7	$199.79	10.456%	$220.68	$220.68	$220.70	$220.70
7 purchase totals =	$893.25		$978.3975	$978.41	$978.45	$978.40