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	$152.50	12.424%	$171.4466	$171.45	$171.45	$171.40
Purchase #2	$59.83	7.843%	$64.5225	$64.52	$64.50	$64.50
Purchase #3	$92.99	7.873%	$100.3111	$100.31	$100.30	$100.30
Purchase #4	$14.78	5.610%	$15.6092	$15.61	$15.60	$15.60
Purchase #5	$17.88	6.284%	$19.0036	$19.00	$19.00	$19.00
Purchase #6	$99.26	9.782%	$108.9696	$108.97	$108.95	$109.00
Purchase #7	$25.69	9.870%	$28.2256	$28.23	$28.25	$28.20
7 purchase totals =	$462.93		$508.0882	$508.09	$508.05	$508.00