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	$191.98	13.326%	$217.5633	$217.56	$217.55	$217.60
Purchase #2	$53.36	3.224%	$55.0803	$55.08	$55.10	$55.10
Purchase #3	$40.25	5.275%	$42.3732	$42.37	$42.35	$42.40
Purchase #4	$39.37	11.157%	$43.7625	$43.76	$43.75	$43.80
Purchase #5	$20.81	5.380%	$21.9296	$21.93	$21.95	$21.90
Purchase #6	$94.48	11.367%	$105.2195	$105.22	$105.20	$105.20
Purchase #7	$94.91	9.508%	$103.934	$103.93	$103.95	$103.90
7 purchase totals =	$535.16		$589.8624	$589.85	$589.85	$589.90