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	$51.60	4.817%	$54.0856	$54.09	$54.10	$54.10
Purchase #2	$156.25	7.150%	$167.4219	$167.42	$167.40	$167.40
Purchase #3	$104.99	10.113%	$115.6076	$115.61	$115.60	$115.60
Purchase #4	$30.54	8.256%	$33.0614	$33.06	$33.05	$33.10
Purchase #5	$59.33	13.670%	$67.4404	$67.44	$67.45	$67.40
Purchase #6	$17.80	10.625%	$19.6913	$19.69	$19.70	$19.70
Purchase #7	$55.39	6.558%	$59.0225	$59.02	$59.00	$59.00
7 purchase totals =	$475.90		$516.3307	$516.33	$516.30	$516.30