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	$42.35	5.331%	$44.6077	$44.61	$44.60	$44.60
Purchase #2	$223.80	11.461%	$249.4497	$249.45	$249.45	$249.40
Purchase #3	$89.40	11.663%	$99.8267	$99.83	$99.85	$99.80
Purchase #4	$23.81	13.739%	$27.0813	$27.08	$27.10	$27.10
Purchase #5	$72.67	11.251%	$80.8461	$80.85	$80.85	$80.80
Purchase #6	$152.50	6.240%	$162.016	$162.02	$162.00	$162.00
Purchase #7	$230.93	5.537%	$243.7166	$243.72	$243.70	$243.70
7 purchase totals =	$835.46		$907.5441	$907.56	$907.55	$907.40