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	$21.38	12.344%	$24.0191	$24.02	$24.00	$24.00
Purchase #2	$211.82	8.305%	$229.4117	$229.41	$229.40	$229.40
Purchase #3	$182.33	10.171%	$200.8748	$200.87	$200.85	$200.90
Purchase #4	$83.72	7.780%	$90.2334	$90.23	$90.25	$90.20
Purchase #5	$133.65	7.511%	$143.6885	$143.69	$143.70	$143.70
Purchase #6	$123.72	4.873%	$129.7489	$129.75	$129.75	$129.70
Purchase #7	$79.98	3.718%	$82.9537	$82.95	$82.95	$83.00
7 purchase totals =	$836.60		$900.9301	$900.92	$900.90	$900.90