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	$198.54	3.498%	$205.4849	$205.48	$205.50	$205.50
Purchase #2	$153.98	9.183%	$168.12	$168.12	$168.10	$168.10
Purchase #3	$147.47	12.431%	$165.802	$165.80	$165.80	$165.80
Purchase #4	$143.75	3.360%	$148.58	$148.58	$148.60	$148.60
Purchase #5	$84.75	5.782%	$89.6502	$89.65	$89.65	$89.70
Purchase #6	$90.83	13.692%	$103.2664	$103.27	$103.25	$103.30
Purchase #7	$49.43	12.414%	$55.5662	$55.57	$55.55	$55.60
7 purchase totals =	$868.75		$936.4697	$936.47	$936.45	$936.60