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	$183.72	13.424%	$208.3826	$208.38	$208.40	$208.40
Purchase #2	$162.48	10.472%	$179.4949	$179.49	$179.50	$179.50
Purchase #3	$123.65	10.265%	$136.3427	$136.34	$136.35	$136.30
Purchase #4	$67.99	13.671%	$77.2849	$77.28	$77.30	$77.30
Purchase #5	$70.85	3.288%	$73.1795	$73.18	$73.20	$73.20
Purchase #6	$54.73	7.635%	$58.9086	$58.91	$58.90	$58.90
Purchase #7	$38.68	10.853%	$42.8779	$42.88	$42.90	$42.90
7 purchase totals =	$702.10		$776.4711	$776.46	$776.55	$776.50