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	$83.25	3.732%	$86.3569	$86.36	$86.35	$86.40
Purchase #2	$128.44	12.415%	$144.3858	$144.39	$144.40	$144.40
Purchase #3	$89.51	7.583%	$96.2975	$96.30	$96.30	$96.30
Purchase #4	$18.57	3.455%	$19.2116	$19.21	$19.20	$19.20
Purchase #5	$136.61	5.275%	$143.8162	$143.82	$143.80	$143.80
Purchase #6	$19.89	3.780%	$20.6418	$20.64	$20.65	$20.60
Purchase #7	$149.37	3.847%	$155.1163	$155.12	$155.10	$155.10
7 purchase totals =	$625.64		$665.8261	$665.84	$665.80	$665.80