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	$250.56	7.687%	$269.8205	$269.82	$269.80	$269.80
Purchase #2	$193.41	11.334%	$215.3311	$215.33	$215.35	$215.30
Purchase #3	$215.91	12.705%	$243.3414	$243.34	$243.35	$243.30
Purchase #4	$245.52	4.233%	$255.9129	$255.91	$255.90	$255.90
Purchase #5	$250.60	12.283%	$281.3812	$281.38	$281.40	$281.40
Purchase #6	$195.27	5.311%	$205.6408	$205.64	$205.65	$205.60
Purchase #7	$49.33	10.772%	$54.6438	$54.64	$54.65	$54.60
7 purchase totals =	$1,400.60		$1,526.0717	$1,526.06	$1,526.10	$1,525.90