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	$40.59	10.184%	$44.7237	$44.72	$44.70	$44.70
Purchase #2	$175.59	12.381%	$197.3298	$197.33	$197.35	$197.30
Purchase #3	$158.67	6.154%	$168.4346	$168.43	$168.45	$168.40
Purchase #4	$179.86	3.211%	$185.6353	$185.64	$185.65	$185.60
Purchase #5	$180.73	5.498%	$190.6665	$190.67	$190.65	$190.70
Purchase #6	$47.64	12.366%	$53.5312	$53.53	$53.55	$53.50
Purchase #7	$152.94	4.277%	$159.4812	$159.48	$159.50	$159.50
7 purchase totals =	$936.02		$999.8023	$999.80	$999.85	$999.70