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	$17.91	8.642%	$19.4578	$19.46	$19.45	$19.50
Purchase #2	$53.52	3.767%	$55.5361	$55.54	$55.55	$55.50
Purchase #3	$190.28	6.763%	$203.1486	$203.15	$203.15	$203.10
Purchase #4	$129.38	11.374%	$144.0957	$144.10	$144.10	$144.10
Purchase #5	$67.35	6.773%	$71.9116	$71.91	$71.90	$71.90
Purchase #6	$39.40	13.320%	$44.6481	$44.65	$44.65	$44.60
Purchase #7	$53.38	11.166%	$59.3404	$59.34	$59.35	$59.30
7 purchase totals =	$551.22		$598.1383	$598.15	$598.15	$598.00