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	$165.25	12.487%	$185.8848	$185.88	$185.90	$185.90
Purchase #2	$169.54	9.204%	$185.1445	$185.14	$185.15	$185.10
Purchase #3	$81.29	12.326%	$91.3098	$91.31	$91.30	$91.30
Purchase #4	$72.46	5.388%	$76.3641	$76.36	$76.35	$76.40
Purchase #5	$30.32	10.148%	$33.3969	$33.40	$33.40	$33.40
Purchase #6	$106.51	11.682%	$118.9525	$118.95	$118.95	$119.00
Purchase #7	$17.74	3.593%	$18.3774	$18.38	$18.40	$18.40
7 purchase totals =	$643.11		$709.4300	$709.42	$709.45	$709.50