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	$225.69	3.855%	$234.3903	$234.39	$234.40	$234.40
Purchase #2	$29.36	7.405%	$31.5341	$31.53	$31.55	$31.50
Purchase #3	$19.36	6.558%	$20.6296	$20.63	$20.65	$20.60
Purchase #4	$108.29	12.500%	$121.8263	$121.83	$121.85	$121.80
Purchase #5	$74.88	4.547%	$78.2848	$78.28	$78.30	$78.30
Purchase #6	$46.43	10.797%	$51.443	$51.44	$51.45	$51.40
Purchase #7	$240.41	4.383%	$250.9472	$250.95	$250.95	$250.90
7 purchase totals =	$744.42		$789.0553	$789.05	$789.15	$788.90