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	$24.93	3.824%	$25.8833	$25.88	$25.90	$25.90
Purchase #2	$247.85	11.445%	$276.2164	$276.22	$276.20	$276.20
Purchase #3	$121.69	13.659%	$138.3116	$138.31	$138.30	$138.30
Purchase #4	$40.57	5.359%	$42.7441	$42.74	$42.75	$42.70
Purchase #5	$32.62	9.541%	$35.7323	$35.73	$35.75	$35.70
Purchase #6	$86.30	4.433%	$90.1257	$90.13	$90.15	$90.10
Purchase #7	$71.25	9.711%	$78.1691	$78.17	$78.15	$78.20
7 purchase totals =	$625.21		$687.1825	$687.18	$687.20	$687.10