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	$33.96	12.194%	$38.1011	$38.10	$38.10	$38.10
Purchase #2	$95.61	3.543%	$98.9975	$99.00	$99.00	$99.00
Purchase #3	$172.43	10.341%	$190.261	$190.26	$190.25	$190.30
Purchase #4	$164.55	10.202%	$181.3374	$181.34	$181.35	$181.30
Purchase #5	$83.46	12.689%	$94.0502	$94.05	$94.05	$94.10
Purchase #6	$225.58	8.139%	$243.94	$243.94	$243.95	$243.90
Purchase #7	$164.52	6.130%	$174.6051	$174.61	$174.60	$174.60
7 purchase totals =	$940.11		$1,021.2923	$1,021.30	$1,021.30	$1,021.30