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	$224.93	6.156%	$238.7767	$238.78	$238.80	$238.80
Purchase #2	$19.71	8.600%	$21.4051	$21.41	$21.40	$21.40
Purchase #3	$178.32	6.353%	$189.6487	$189.65	$189.65	$189.60
Purchase #4	$49.27	8.145%	$53.283	$53.28	$53.30	$53.30
Purchase #5	$170.59	5.359%	$179.7319	$179.73	$179.75	$179.70
Purchase #6	$99.63	3.507%	$103.124	$103.12	$103.10	$103.10
Purchase #7	$84.70	7.274%	$90.8611	$90.86	$90.85	$90.90
7 purchase totals =	$827.15		$876.8305	$876.83	$876.85	$876.80