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	$102.67	8.485%	$111.3815	$111.38	$111.40	$111.40
Purchase #2	$84.36	6.336%	$89.705	$89.71	$89.70	$89.70
Purchase #3	$11.32	8.580%	$12.2913	$12.29	$12.30	$12.30
Purchase #4	$227.90	6.393%	$242.4696	$242.47	$242.45	$242.50
Purchase #5	$244.84	9.620%	$268.3936	$268.39	$268.40	$268.40
Purchase #6	$11.63	7.479%	$12.4998	$12.50	$12.50	$12.50
Purchase #7	$130.47	11.148%	$145.0148	$145.01	$145.00	$145.00
7 purchase totals =	$813.19		$881.7556	$881.75	$881.75	$881.80