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	$174.64	12.423%	$196.3355	$196.34	$196.35	$196.30
Purchase #2	$140.98	12.633%	$158.79	$158.79	$158.80	$158.80
Purchase #3	$44.76	13.755%	$50.9167	$50.92	$50.90	$50.90
Purchase #4	$165.84	12.512%	$186.5899	$186.59	$186.60	$186.60
Purchase #5	$16.56	13.539%	$18.8021	$18.80	$18.80	$18.80
Purchase #6	$132.26	3.627%	$137.0571	$137.06	$137.05	$137.10
Purchase #7	$59.68	9.627%	$65.4254	$65.43	$65.45	$65.40
7 purchase totals =	$734.72		$813.9167	$813.93	$813.95	$813.90