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	$174.61	11.797%	$195.2087	$195.21	$195.20	$195.20
Purchase #2	$151.46	4.868%	$158.8331	$158.83	$158.85	$158.80
Purchase #3	$49.63	12.806%	$55.9856	$55.99	$56.00	$56.00
Purchase #4	$108.86	7.608%	$117.1421	$117.14	$117.15	$117.10
Purchase #5	$19.88	6.790%	$21.2299	$21.23	$21.25	$21.20
Purchase #6	$38.91	8.256%	$42.1224	$42.12	$42.10	$42.10
Purchase #7	$70.96	8.534%	$77.0157	$77.02	$77.00	$77.00
7 purchase totals =	$614.31		$667.5375	$667.54	$667.55	$667.40