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	$95.76	3.512%	$99.1231	$99.12	$99.10	$99.10
Purchase #2	$236.77	5.515%	$249.8279	$249.83	$249.85	$249.80
Purchase #3	$42.88	13.721%	$48.7636	$48.76	$48.75	$48.80
Purchase #4	$228.45	5.265%	$240.4779	$240.48	$240.50	$240.50
Purchase #5	$6.62	11.631%	$7.39	$7.39	$7.40	$7.40
Purchase #6	$151.73	13.611%	$172.382	$172.38	$172.40	$172.40
Purchase #7	$117.77	8.483%	$127.7604	$127.76	$127.75	$127.80
7 purchase totals =	$879.98		$945.7249	$945.72	$945.75	$945.80