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	$91.75	8.269%	$99.3368	$99.34	$99.35	$99.30
Purchase #2	$54.29	12.292%	$60.9633	$60.96	$60.95	$61.00
Purchase #3	$80.32	9.873%	$88.25	$88.25	$88.25	$88.30
Purchase #4	$167.38	13.451%	$189.8943	$189.89	$189.90	$189.90
Purchase #5	$90.76	4.852%	$95.1637	$95.16	$95.15	$95.20
Purchase #6	$167.59	12.636%	$188.7667	$188.77	$188.75	$188.80
Purchase #7	$204.39	13.405%	$231.7885	$231.79	$231.80	$231.80
7 purchase totals =	$856.48		$954.1633	$954.16	$954.15	$954.30