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	$119.62	13.168%	$135.3716	$135.37	$135.35	$135.40
Purchase #2	$41.89	13.457%	$47.5271	$47.53	$47.55	$47.50
Purchase #3	$139.92	11.584%	$156.1283	$156.13	$156.15	$156.10
Purchase #4	$49.90	9.407%	$54.5941	$54.59	$54.60	$54.60
Purchase #5	$57.77	9.527%	$63.2737	$63.27	$63.25	$63.30
Purchase #6	$40.53	10.327%	$44.7155	$44.72	$44.70	$44.70
Purchase #7	$55.89	6.472%	$59.5072	$59.51	$59.50	$59.50
7 purchase totals =	$505.52		$561.1175	$561.12	$561.10	$561.10