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	$18.31	9.138%	$19.9832	$19.98	$20.00	$20.00
Purchase #2	$63.59	3.196%	$65.6223	$65.62	$65.60	$65.60
Purchase #3	$70.79	11.557%	$78.9712	$78.97	$78.95	$79.00
Purchase #4	$219.87	4.751%	$230.316	$230.32	$230.30	$230.30
Purchase #5	$63.71	12.312%	$71.554	$71.55	$71.55	$71.60
Purchase #6	$247.76	7.267%	$265.7647	$265.76	$265.75	$265.80
Purchase #7	$148.43	10.663%	$164.2571	$164.26	$164.25	$164.30
7 purchase totals =	$832.46		$896.4685	$896.46	$896.40	$896.60