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	$32.69	3.671%	$33.89	$33.89	$33.90	$33.90
Purchase #2	$202.45	12.152%	$227.0517	$227.05	$227.05	$227.10
Purchase #3	$169.89	12.413%	$190.9784	$190.98	$191.00	$191.00
Purchase #4	$139.72	8.243%	$151.2371	$151.24	$151.25	$151.20
Purchase #5	$171.82	3.777%	$178.3096	$178.31	$178.30	$178.30
Purchase #6	$6.77	9.305%	$7.3999	$7.40	$7.40	$7.40
Purchase #7	$58.26	6.622%	$62.118	$62.12	$62.10	$62.10
7 purchase totals =	$781.60		$850.9847	$850.99	$851.00	$851.00