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	$158.44	5.652%	$167.395	$167.40	$167.40	$167.40
Purchase #2	$83.73	7.586%	$90.0818	$90.08	$90.10	$90.10
Purchase #3	$221.86	5.364%	$233.7606	$233.76	$233.75	$233.80
Purchase #4	$168.78	12.606%	$190.0564	$190.06	$190.05	$190.10
Purchase #5	$16.43	5.640%	$17.3567	$17.36	$17.35	$17.40
Purchase #6	$97.32	9.244%	$106.3163	$106.32	$106.30	$106.30
Purchase #7	$36.61	10.524%	$40.4628	$40.46	$40.45	$40.50
7 purchase totals =	$783.17		$845.4296	$845.44	$845.40	$845.60