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	$81.48	11.195%	$90.6017	$90.60	$90.60	$90.60
Purchase #2	$185.96	9.818%	$204.2176	$204.22	$204.20	$204.20
Purchase #3	$174.52	11.279%	$194.2041	$194.20	$194.20	$194.20
Purchase #4	$153.83	10.173%	$169.4791	$169.48	$169.50	$169.50
Purchase #5	$42.57	12.820%	$48.0275	$48.03	$48.05	$48.00
Purchase #6	$161.64	10.801%	$179.0987	$179.10	$179.10	$179.10
Purchase #7	$234.51	13.536%	$266.2533	$266.25	$266.25	$266.30
7 purchase totals =	$1,034.51		$1,151.8820	$1,151.88	$1,151.90	$1,151.90