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	$51.30	11.263%	$57.0779	$57.08	$57.10	$57.10
Purchase #2	$171.29	8.395%	$185.6698	$185.67	$185.65	$185.70
Purchase #3	$176.59	4.270%	$184.1304	$184.13	$184.15	$184.10
Purchase #4	$120.56	4.563%	$126.0612	$126.06	$126.05	$126.10
Purchase #5	$82.51	8.578%	$89.5877	$89.59	$89.60	$89.60
Purchase #6	$41.34	7.378%	$44.3901	$44.39	$44.40	$44.40
Purchase #7	$36.44	13.343%	$41.3022	$41.30	$41.30	$41.30
7 purchase totals =	$680.03		$728.2193	$728.22	$728.25	$728.30