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	$115.63	6.356%	$122.9794	$122.98	$123.00	$123.00
Purchase #2	$60.51	3.420%	$62.5794	$62.58	$62.60	$62.60
Purchase #3	$42.89	11.661%	$47.8914	$47.89	$47.90	$47.90
Purchase #4	$127.27	8.446%	$138.0192	$138.02	$138.00	$138.00
Purchase #5	$139.33	5.773%	$147.3735	$147.37	$147.35	$147.40
Purchase #6	$82.78	3.705%	$85.847	$85.85	$85.85	$85.80
Purchase #7	$69.34	3.500%	$71.7669	$71.77	$71.75	$71.80
7 purchase totals =	$637.75		$676.4568	$676.46	$676.45	$676.50