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	$131.70	6.421%	$140.1565	$140.16	$140.15	$140.20
Purchase #2	$175.25	5.510%	$184.9063	$184.91	$184.90	$184.90
Purchase #3	$144.44	10.467%	$159.5585	$159.56	$159.55	$159.60
Purchase #4	$250.89	5.392%	$264.418	$264.42	$264.40	$264.40
Purchase #5	$63.60	13.734%	$72.3348	$72.33	$72.35	$72.30
Purchase #6	$109.78	8.353%	$118.9499	$118.95	$118.95	$118.90
Purchase #7	$115.63	13.368%	$131.0874	$131.09	$131.10	$131.10
7 purchase totals =	$991.29		$1,071.4114	$1,071.42	$1,071.40	$1,071.40