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	$144.26	6.379%	$153.4623	$153.46	$153.45	$153.50
Purchase #2	$51.38	5.192%	$54.0476	$54.05	$54.05	$54.00
Purchase #3	$97.48	7.745%	$105.0298	$105.03	$105.05	$105.00
Purchase #4	$211.65	12.839%	$238.8237	$238.82	$238.80	$238.80
Purchase #5	$168.64	9.704%	$185.0048	$185.00	$185.00	$185.00
Purchase #6	$50.90	9.372%	$55.6703	$55.67	$55.65	$55.70
Purchase #7	$52.41	12.743%	$59.0886	$59.09	$59.10	$59.10
7 purchase totals =	$776.72		$851.1271	$851.12	$851.10	$851.10