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	$135.87	10.545%	$150.1975	$150.20	$150.20	$150.20
Purchase #2	$48.51	12.369%	$54.5102	$54.51	$54.50	$54.50
Purchase #3	$244.27	7.166%	$261.7744	$261.77	$261.75	$261.80
Purchase #4	$196.89	12.576%	$221.6509	$221.65	$221.65	$221.70
Purchase #5	$54.37	11.218%	$60.4692	$60.47	$60.45	$60.50
Purchase #6	$66.37	3.119%	$68.4401	$68.44	$68.45	$68.40
Purchase #7	$176.69	5.111%	$185.7206	$185.72	$185.70	$185.70
7 purchase totals =	$922.97		$1,002.7629	$1,002.76	$1,002.70	$1,002.80