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	8.433%	$189.3674	$189.37	$189.35	$189.40
Purchase #2	$40.42	12.330%	$45.4038	$45.40	$45.40	$45.40
Purchase #3	$82.95	4.220%	$86.4505	$86.45	$86.45	$86.50
Purchase #4	$36.28	11.737%	$40.5382	$40.54	$40.55	$40.50
Purchase #5	$245.43	3.235%	$253.3697	$253.37	$253.35	$253.40
Purchase #6	$40.81	11.688%	$45.5799	$45.58	$45.60	$45.60
Purchase #7	$149.95	12.257%	$168.3294	$168.33	$168.35	$168.30
7 purchase totals =	$770.48		$829.0389	$829.04	$829.05	$829.10