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	$76.80	10.712%	$85.0268	$85.03	$85.05	$85.00
Purchase #2	$40.90	12.184%	$45.8833	$45.88	$45.90	$45.90
Purchase #3	$33.56	6.196%	$35.6394	$35.64	$35.65	$35.60
Purchase #4	$94.92	9.507%	$103.944	$103.94	$103.95	$103.90
Purchase #5	$116.89	9.442%	$127.9268	$127.93	$127.95	$127.90
Purchase #6	$209.44	9.163%	$228.631	$228.63	$228.65	$228.60
Purchase #7	$197.92	9.285%	$216.2969	$216.30	$216.30	$216.30
7 purchase totals =	$770.43		$843.3482	$843.35	$843.45	$843.20