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	$22.65	4.266%	$23.6162	$23.62	$23.60	$23.60
Purchase #2	$138.54	12.623%	$156.0279	$156.03	$156.05	$156.00
Purchase #3	$187.84	4.731%	$196.7267	$196.73	$196.75	$196.70
Purchase #4	$33.34	12.512%	$37.5115	$37.51	$37.50	$37.50
Purchase #5	$125.76	6.274%	$133.6502	$133.65	$133.65	$133.70
Purchase #6	$50.94	6.118%	$54.0565	$54.06	$54.05	$54.10
Purchase #7	$36.46	4.787%	$38.2053	$38.21	$38.20	$38.20
7 purchase totals =	$595.53		$639.7943	$639.81	$639.80	$639.80