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	$22.80	12.309%	$25.6065	$25.61	$25.60	$25.60
Purchase #2	$234.72	11.419%	$261.5227	$261.52	$261.50	$261.50
Purchase #3	$194.44	8.706%	$211.3679	$211.37	$211.35	$211.40
Purchase #4	$199.28	8.665%	$216.5476	$216.55	$216.55	$216.50
Purchase #5	$99.87	10.166%	$110.0228	$110.02	$110.00	$110.00
Purchase #6	$33.53	4.857%	$35.1586	$35.16	$35.15	$35.20
Purchase #7	$104.83	12.449%	$117.8803	$117.88	$117.90	$117.90
7 purchase totals =	$889.47		$978.1064	$978.11	$978.05	$978.10