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	$27.65	9.198%	$30.1932	$30.19	$30.20	$30.20
Purchase #2	$191.46	4.625%	$200.315	$200.32	$200.30	$200.30
Purchase #3	$96.76	13.386%	$109.7123	$109.71	$109.70	$109.70
Purchase #4	$38.29	3.652%	$39.6884	$39.69	$39.70	$39.70
Purchase #5	$212.84	10.125%	$234.3901	$234.39	$234.40	$234.40
Purchase #6	$6.84	6.818%	$7.3064	$7.31	$7.30	$7.30
Purchase #7	$55.72	6.819%	$59.5195	$59.52	$59.50	$59.50
7 purchase totals =	$629.56		$681.1249	$681.13	$681.10	$681.10