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	$200.69	11.524%	$223.8175	$223.82	$223.80	$223.80
Purchase #2	$141.94	5.481%	$149.7197	$149.72	$149.70	$149.70
Purchase #3	$66.60	13.850%	$75.8241	$75.82	$75.80	$75.80
Purchase #4	$180.93	10.470%	$199.8734	$199.87	$199.85	$199.90
Purchase #5	$53.33	6.736%	$56.9223	$56.92	$56.90	$56.90
Purchase #6	$65.96	9.460%	$72.1998	$72.20	$72.20	$72.20
Purchase #7	$9.33	11.711%	$10.4226	$10.42	$10.40	$10.40
7 purchase totals =	$718.78		$788.7794	$788.77	$788.65	$788.70