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	$130.49	5.828%	$138.095	$138.10	$138.10	$138.10
Purchase #2	$143.73	6.832%	$153.5496	$153.55	$153.55	$153.50
Purchase #3	$95.39	5.790%	$100.9131	$100.91	$100.90	$100.90
Purchase #4	$247.72	7.350%	$265.9274	$265.93	$265.95	$265.90
Purchase #5	$128.41	11.471%	$143.1399	$143.14	$143.15	$143.10
Purchase #6	$81.49	9.514%	$89.243	$89.24	$89.25	$89.20
Purchase #7	$6.66	6.763%	$7.1104	$7.11	$7.10	$7.10
7 purchase totals =	$833.89		$897.9784	$897.98	$898.00	$897.80