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	$241.43	6.320%	$256.6884	$256.69	$256.70	$256.70
Purchase #2	$77.71	6.148%	$82.4876	$82.49	$82.50	$82.50
Purchase #3	$112.46	7.642%	$121.0542	$121.05	$121.05	$121.10
Purchase #4	$79.86	11.602%	$89.1254	$89.13	$89.15	$89.10
Purchase #5	$141.61	6.414%	$150.6929	$150.69	$150.70	$150.70
Purchase #6	$197.59	4.139%	$205.7683	$205.77	$205.75	$205.80
Purchase #7	$233.36	7.697%	$251.3217	$251.32	$251.30	$251.30
7 purchase totals =	$1,084.02		$1,157.1385	$1,157.14	$1,157.15	$1,157.20