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	$38.79	9.245%	$42.3761	$42.38	$42.40	$42.40
Purchase #2	$159.45	4.711%	$166.9617	$166.96	$166.95	$167.00
Purchase #3	$135.41	11.356%	$150.7872	$150.79	$150.80	$150.80
Purchase #4	$129.65	11.634%	$144.7335	$144.73	$144.75	$144.70
Purchase #5	$42.70	8.821%	$46.4666	$46.47	$46.45	$46.50
Purchase #6	$35.82	5.754%	$37.8811	$37.88	$37.90	$37.90
Purchase #7	$43.69	11.755%	$48.8258	$48.83	$48.85	$48.80
7 purchase totals =	$585.51		$638.0320	$638.04	$638.10	$638.10