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	$81.66	9.354%	$89.2985	$89.30	$89.30	$89.30
Purchase #2	$188.31	3.812%	$195.4884	$195.49	$195.50	$195.50
Purchase #3	$103.46	9.174%	$112.9514	$112.95	$112.95	$113.00
Purchase #4	$52.56	8.286%	$56.9151	$56.92	$56.90	$56.90
Purchase #5	$97.50	13.748%	$110.9043	$110.90	$110.90	$110.90
Purchase #6	$83.97	7.270%	$90.0746	$90.07	$90.05	$90.10
Purchase #7	$152.47	10.623%	$168.6669	$168.67	$168.65	$168.70
7 purchase totals =	$759.93		$824.2992	$824.30	$824.25	$824.40