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	$231.48	10.102%	$254.8641	$254.86	$254.85	$254.90
Purchase #2	$222.30	4.281%	$231.8167	$231.82	$231.80	$231.80
Purchase #3	$117.76	5.207%	$123.8918	$123.89	$123.90	$123.90
Purchase #4	$110.88	4.811%	$116.2144	$116.21	$116.20	$116.20
Purchase #5	$151.60	9.231%	$165.5942	$165.59	$165.60	$165.60
Purchase #6	$101.50	4.376%	$105.9416	$105.94	$105.95	$105.90
Purchase #7	$248.57	12.317%	$279.1864	$279.19	$279.20	$279.20
7 purchase totals =	$1,184.09		$1,277.5092	$1,277.50	$1,277.50	$1,277.50