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	$19.54	11.192%	$21.7269	$21.73	$21.75	$21.70
Purchase #2	$58.43	11.823%	$65.3382	$65.34	$65.35	$65.30
Purchase #3	$187.75	3.387%	$194.1091	$194.11	$194.10	$194.10
Purchase #4	$96.71	7.162%	$103.6364	$103.64	$103.65	$103.60
Purchase #5	$157.57	9.677%	$172.818	$172.82	$172.80	$172.80
Purchase #6	$217.73	10.152%	$239.8339	$239.83	$239.85	$239.80
Purchase #7	$186.61	10.696%	$206.5698	$206.57	$206.55	$206.60
7 purchase totals =	$924.34		$1,004.0323	$1,004.04	$1,004.05	$1,003.90