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	$240.85	12.171%	$270.1639	$270.16	$270.15	$270.20
Purchase #2	$76.45	12.632%	$86.1072	$86.11	$86.10	$86.10
Purchase #3	$51.28	4.558%	$53.6173	$53.62	$53.60	$53.60
Purchase #4	$32.78	7.481%	$35.2323	$35.23	$35.25	$35.20
Purchase #5	$68.46	4.494%	$71.5366	$71.54	$71.55	$71.50
Purchase #6	$115.31	13.166%	$130.4917	$130.49	$130.50	$130.50
Purchase #7	$178.81	5.606%	$188.8341	$188.83	$188.85	$188.80
7 purchase totals =	$763.94		$835.9831	$835.98	$836.00	$835.90