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	$117.84	5.539%	$124.3672	$124.37	$124.35	$124.40
Purchase #2	$55.33	7.535%	$59.4991	$59.50	$59.50	$59.50
Purchase #3	$173.42	10.670%	$191.9239	$191.92	$191.90	$191.90
Purchase #4	$137.81	3.399%	$142.4942	$142.49	$142.50	$142.50
Purchase #5	$198.72	3.872%	$206.4144	$206.41	$206.40	$206.40
Purchase #6	$65.31	9.508%	$71.5197	$71.52	$71.50	$71.50
Purchase #7	$47.99	7.169%	$51.4304	$51.43	$51.45	$51.40
7 purchase totals =	$796.42		$847.6489	$847.64	$847.60	$847.60