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	$16.88	9.771%	$18.5293	$18.53	$18.55	$18.50
Purchase #2	$230.31	12.679%	$259.511	$259.51	$259.50	$259.50
Purchase #3	$98.91	3.106%	$101.9821	$101.98	$102.00	$102.00
Purchase #4	$250.45	3.747%	$259.8344	$259.83	$259.85	$259.80
Purchase #5	$156.97	8.486%	$170.2905	$170.29	$170.30	$170.30
Purchase #6	$88.67	12.173%	$99.4638	$99.46	$99.45	$99.50
Purchase #7	$103.53	12.752%	$116.7321	$116.73	$116.75	$116.70
7 purchase totals =	$945.72		$1,026.3432	$1,026.33	$1,026.40	$1,026.30