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	$141.36	3.411%	$146.1818	$146.18	$146.20	$146.20
Purchase #2	$90.31	9.227%	$98.6429	$98.64	$98.65	$98.60
Purchase #3	$35.44	11.733%	$39.5982	$39.60	$39.60	$39.60
Purchase #4	$98.62	8.442%	$106.9455	$106.95	$106.95	$106.90
Purchase #5	$187.93	4.714%	$196.789	$196.79	$196.80	$196.80
Purchase #6	$187.34	10.780%	$207.5353	$207.54	$207.55	$207.50
Purchase #7	$171.51	6.408%	$182.5004	$182.50	$182.50	$182.50
7 purchase totals =	$912.51		$978.1931	$978.20	$978.25	$978.10