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	$123.41	5.719%	$130.4678	$130.47	$130.45	$130.50
Purchase #2	$79.29	11.601%	$88.4884	$88.49	$88.50	$88.50
Purchase #3	$60.63	11.602%	$67.6643	$67.66	$67.65	$67.70
Purchase #4	$7.66	6.783%	$8.1796	$8.18	$8.20	$8.20
Purchase #5	$115.83	6.737%	$123.6335	$123.63	$123.65	$123.60
Purchase #6	$39.48	5.850%	$41.7896	$41.79	$41.80	$41.80
Purchase #7	$165.82	12.260%	$186.1495	$186.15	$186.15	$186.10
7 purchase totals =	$592.12		$646.3727	$646.37	$646.40	$646.40