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	$228.88	11.576%	$255.3751	$255.38	$255.40	$255.40
Purchase #2	$180.94	10.350%	$199.6673	$199.67	$199.65	$199.70
Purchase #3	$6.58	13.812%	$7.4888	$7.49	$7.50	$7.50
Purchase #4	$238.39	8.350%	$258.2956	$258.30	$258.30	$258.30
Purchase #5	$50.32	13.831%	$57.2798	$57.28	$57.30	$57.30
Purchase #6	$6.81	7.541%	$7.3235	$7.32	$7.30	$7.30
Purchase #7	$126.48	10.216%	$139.4012	$139.40	$139.40	$139.40
7 purchase totals =	$838.40		$924.8313	$924.84	$924.85	$924.90