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	$151.57	13.704%	$172.3412	$172.34	$172.35	$172.30
Purchase #2	$103.61	10.850%	$114.8517	$114.85	$114.85	$114.90
Purchase #3	$156.63	10.326%	$172.8036	$172.80	$172.80	$172.80
Purchase #4	$6.77	4.223%	$7.0559	$7.06	$7.05	$7.10
Purchase #5	$43.63	3.407%	$45.1165	$45.12	$45.10	$45.10
Purchase #6	$11.35	13.402%	$12.8711	$12.87	$12.85	$12.90
Purchase #7	$113.86	3.212%	$117.5172	$117.52	$117.50	$117.50
7 purchase totals =	$587.42		$642.5572	$642.56	$642.50	$642.60