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	$20.90	6.678%	$22.2957	$22.30	$22.30	$22.30
Purchase #2	$63.40	13.455%	$71.9305	$71.93	$71.95	$71.90
Purchase #3	$8.49	3.671%	$8.8017	$8.80	$8.80	$8.80
Purchase #4	$52.52	13.679%	$59.7042	$59.70	$59.70	$59.70
Purchase #5	$78.43	13.669%	$89.1506	$89.15	$89.15	$89.20
Purchase #6	$187.70	12.711%	$211.5585	$211.56	$211.55	$211.60
Purchase #7	$148.30	12.871%	$167.3877	$167.39	$167.40	$167.40
7 purchase totals =	$559.74		$630.8289	$630.83	$630.85	$630.90