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	$95.85	3.803%	$99.4952	$99.50	$99.50	$99.50
Purchase #2	$145.84	10.250%	$160.7886	$160.79	$160.80	$160.80
Purchase #3	$98.89	5.251%	$104.0827	$104.08	$104.10	$104.10
Purchase #4	$68.26	11.482%	$76.0976	$76.10	$76.10	$76.10
Purchase #5	$126.92	3.577%	$131.4599	$131.46	$131.45	$131.50
Purchase #6	$242.48	10.216%	$267.2518	$267.25	$267.25	$267.30
Purchase #7	$116.59	12.307%	$130.9387	$130.94	$130.95	$130.90
7 purchase totals =	$894.83		$970.1145	$970.12	$970.15	$970.20