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	$19.50	4.609%	$20.3988	$20.40	$20.40	$20.40
Purchase #2	$10.73	10.796%	$11.8884	$11.89	$11.90	$11.90
Purchase #3	$110.67	5.235%	$116.4636	$116.46	$116.45	$116.50
Purchase #4	$81.62	10.167%	$89.9183	$89.92	$89.90	$89.90
Purchase #5	$100.33	8.840%	$109.1992	$109.20	$109.20	$109.20
Purchase #6	$70.79	7.568%	$76.1474	$76.15	$76.15	$76.10
Purchase #7	$152.45	10.274%	$168.1127	$168.11	$168.10	$168.10
7 purchase totals =	$546.09		$592.1284	$592.13	$592.10	$592.10