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	$132.97	11.839%	$148.7123	$148.71	$148.70	$148.70
Purchase #2	$57.77	13.789%	$65.7359	$65.74	$65.75	$65.70
Purchase #3	$47.41	5.781%	$50.1508	$50.15	$50.15	$50.20
Purchase #4	$68.86	4.382%	$71.8774	$71.88	$71.90	$71.90
Purchase #5	$80.78	13.739%	$91.8784	$91.88	$91.90	$91.90
Purchase #6	$91.85	8.818%	$99.9493	$99.95	$99.95	$99.90
Purchase #7	$104.75	12.110%	$117.4352	$117.44	$117.45	$117.40
7 purchase totals =	$584.39		$645.7393	$645.75	$645.80	$645.70