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	$31.29	6.601%	$33.3555	$33.36	$33.35	$33.40
Purchase #2	$44.48	13.371%	$50.4274	$50.43	$50.45	$50.40
Purchase #3	$53.57	10.594%	$59.2452	$59.25	$59.25	$59.20
Purchase #4	$57.73	13.753%	$65.6696	$65.67	$65.65	$65.70
Purchase #5	$143.39	4.195%	$149.4052	$149.41	$149.40	$149.40
Purchase #6	$76.52	13.257%	$86.6643	$86.66	$86.65	$86.70
Purchase #7	$184.98	7.528%	$198.9053	$198.91	$198.90	$198.90
7 purchase totals =	$591.96		$643.6725	$643.69	$643.65	$643.70