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	$159.75	5.740%	$168.9197	$168.92	$168.90	$168.90
Purchase #2	$231.90	12.134%	$260.0387	$260.04	$260.05	$260.00
Purchase #3	$198.29	12.528%	$223.1318	$223.13	$223.15	$223.10
Purchase #4	$220.83	12.339%	$248.0782	$248.08	$248.10	$248.10
Purchase #5	$103.58	7.255%	$111.0947	$111.09	$111.10	$111.10
Purchase #6	$152.56	12.107%	$171.0304	$171.03	$171.05	$171.00
Purchase #7	$34.64	12.370%	$38.925	$38.93	$38.95	$38.90
7 purchase totals =	$1,101.55		$1,221.2185	$1,221.22	$1,221.30	$1,221.10