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	$91.42	8.304%	$99.0115	$99.01	$99.00	$99.00
Purchase #2	$91.38	8.693%	$99.3237	$99.32	$99.30	$99.30
Purchase #3	$242.37	13.312%	$274.6343	$274.63	$274.65	$274.60
Purchase #4	$155.74	3.228%	$160.7673	$160.77	$160.75	$160.80
Purchase #5	$133.95	7.561%	$144.078	$144.08	$144.10	$144.10
Purchase #6	$89.35	9.484%	$97.824	$97.82	$97.80	$97.80
Purchase #7	$211.84	11.644%	$236.5066	$236.51	$236.50	$236.50
7 purchase totals =	$1,016.05		$1,112.1454	$1,112.14	$1,112.10	$1,112.10