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	$199.28	13.814%	$226.8085	$226.81	$226.80	$226.80
Purchase #2	$83.87	8.409%	$90.9226	$90.92	$90.90	$90.90
Purchase #3	$120.45	12.778%	$135.8411	$135.84	$135.85	$135.80
Purchase #4	$152.59	7.846%	$164.5622	$164.56	$164.55	$164.60
Purchase #5	$91.30	7.629%	$98.2653	$98.27	$98.25	$98.30
Purchase #6	$142.25	5.648%	$150.2843	$150.28	$150.30	$150.30
Purchase #7	$205.41	3.616%	$212.8376	$212.84	$212.85	$212.80
7 purchase totals =	$995.15		$1,079.5216	$1,079.52	$1,079.50	$1,079.50