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	$170.85	10.711%	$189.1497	$189.15	$189.15	$189.10
Purchase #2	$52.62	9.388%	$57.56	$57.56	$57.55	$57.60
Purchase #3	$174.49	9.704%	$191.4225	$191.42	$191.40	$191.40
Purchase #4	$227.92	12.261%	$255.8653	$255.87	$255.85	$255.90
Purchase #5	$19.53	13.812%	$22.2275	$22.23	$22.25	$22.20
Purchase #6	$209.25	9.132%	$228.3587	$228.36	$228.35	$228.40
Purchase #7	$178.82	11.818%	$199.9529	$199.95	$199.95	$200.00
7 purchase totals =	$1,033.48		$1,144.5366	$1,144.54	$1,144.50	$1,144.60