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	$51.31	9.809%	$56.343	$56.34	$56.35	$56.30
Purchase #2	$247.63	11.785%	$276.8132	$276.81	$276.80	$276.80
Purchase #3	$123.60	12.336%	$138.8473	$138.85	$138.85	$138.80
Purchase #4	$244.72	3.567%	$253.4492	$253.45	$253.45	$253.40
Purchase #5	$39.89	7.341%	$42.8183	$42.82	$42.80	$42.80
Purchase #6	$200.86	6.816%	$214.5506	$214.55	$214.55	$214.60
Purchase #7	$100.68	10.144%	$110.893	$110.89	$110.90	$110.90
7 purchase totals =	$1,008.69		$1,093.7146	$1,093.71	$1,093.70	$1,093.60