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	$240.75	10.854%	$266.881	$266.88	$266.90	$266.90
Purchase #2	$187.87	9.279%	$205.3025	$205.30	$205.30	$205.30
Purchase #3	$83.94	6.201%	$89.1451	$89.15	$89.15	$89.10
Purchase #4	$235.40	5.103%	$247.4125	$247.41	$247.40	$247.40
Purchase #5	$6.76	4.180%	$7.0426	$7.04	$7.05	$7.00
Purchase #6	$147.71	7.203%	$158.3496	$158.35	$158.35	$158.30
Purchase #7	$76.96	7.846%	$82.9983	$83.00	$83.00	$83.00
7 purchase totals =	$979.39		$1,057.1316	$1,057.13	$1,057.15	$1,057.00