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	$139.66	5.154%	$146.8581	$146.86	$146.85	$146.90
Purchase #2	$147.33	7.838%	$158.8777	$158.88	$158.90	$158.90
Purchase #3	$125.34	13.391%	$142.1243	$142.12	$142.10	$142.10
Purchase #4	$39.66	10.504%	$43.8259	$43.83	$43.85	$43.80
Purchase #5	$95.82	3.266%	$98.9495	$98.95	$98.95	$98.90
Purchase #6	$165.34	11.457%	$184.283	$184.28	$184.30	$184.30
Purchase #7	$128.71	3.653%	$133.4118	$133.41	$133.40	$133.40
7 purchase totals =	$841.86		$908.3303	$908.33	$908.35	$908.30