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	$193.80	13.221%	$219.4223	$219.42	$219.40	$219.40
Purchase #2	$145.50	13.368%	$164.9504	$164.95	$164.95	$165.00
Purchase #3	$54.71	4.531%	$57.1889	$57.19	$57.20	$57.20
Purchase #4	$215.98	10.326%	$238.2821	$238.28	$238.30	$238.30
Purchase #5	$38.88	10.667%	$43.0273	$43.03	$43.05	$43.00
Purchase #6	$91.69	12.765%	$103.3942	$103.39	$103.40	$103.40
Purchase #7	$67.75	5.469%	$71.4552	$71.46	$71.45	$71.50
7 purchase totals =	$808.31		$897.7204	$897.72	$897.75	$897.80