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	$26.79	9.313%	$29.285	$29.29	$29.30	$29.30
Purchase #2	$190.70	9.842%	$209.4687	$209.47	$209.45	$209.50
Purchase #3	$226.57	6.455%	$241.1951	$241.20	$241.20	$241.20
Purchase #4	$41.64	9.183%	$45.4638	$45.46	$45.45	$45.50
Purchase #5	$68.51	6.390%	$72.8878	$72.89	$72.90	$72.90
Purchase #6	$206.31	3.390%	$213.3039	$213.30	$213.30	$213.30
Purchase #7	$209.66	3.608%	$217.2245	$217.22	$217.20	$217.20
7 purchase totals =	$970.18		$1,028.8288	$1,028.83	$1,028.80	$1,028.90