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	$32.86	7.699%	$35.3899	$35.39	$35.40	$35.40
Purchase #2	$247.77	9.719%	$271.8508	$271.85	$271.85	$271.90
Purchase #3	$171.83	12.280%	$192.9307	$192.93	$192.95	$192.90
Purchase #4	$206.50	13.381%	$234.1318	$234.13	$234.15	$234.10
Purchase #5	$214.91	6.456%	$228.7846	$228.78	$228.80	$228.80
Purchase #6	$156.86	9.340%	$171.5107	$171.51	$171.50	$171.50
Purchase #7	$112.53	7.211%	$120.6445	$120.64	$120.65	$120.60
7 purchase totals =	$1,143.26		$1,255.2430	$1,255.23	$1,255.30	$1,255.20