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	$89.86	11.196%	$99.9207	$99.92	$99.90	$99.90
Purchase #2	$72.61	10.176%	$79.9988	$80.00	$80.00	$80.00
Purchase #3	$88.67	6.412%	$94.3555	$94.36	$94.35	$94.40
Purchase #4	$172.25	11.112%	$191.3904	$191.39	$191.40	$191.40
Purchase #5	$85.39	9.366%	$93.3876	$93.39	$93.40	$93.40
Purchase #6	$83.37	10.719%	$92.3064	$92.31	$92.30	$92.30
Purchase #7	$34.31	5.807%	$36.3024	$36.30	$36.30	$36.30
7 purchase totals =	$626.46		$687.6618	$687.67	$687.65	$687.70