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	$78.29	12.436%	$88.0261	$88.03	$88.05	$88.00
Purchase #2	$103.36	4.856%	$108.3792	$108.38	$108.40	$108.40
Purchase #3	$97.61	9.234%	$106.6233	$106.62	$106.60	$106.60
Purchase #4	$149.44	4.404%	$156.0213	$156.02	$156.00	$156.00
Purchase #5	$111.77	13.372%	$126.7159	$126.72	$126.70	$126.70
Purchase #6	$212.91	4.290%	$222.0438	$222.04	$222.05	$222.00
Purchase #7	$97.92	7.746%	$105.5049	$105.50	$105.50	$105.50
7 purchase totals =	$851.30		$913.3145	$913.31	$913.30	$913.20