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	$24.55	13.817%	$27.9421	$27.94	$27.95	$27.90
Purchase #2	$242.98	12.313%	$272.8981	$272.90	$272.90	$272.90
Purchase #3	$153.79	5.672%	$162.513	$162.51	$162.50	$162.50
Purchase #4	$57.50	3.568%	$59.5516	$59.55	$59.55	$59.60
Purchase #5	$237.42	11.404%	$264.4954	$264.50	$264.50	$264.50
Purchase #6	$196.37	5.548%	$207.2646	$207.26	$207.25	$207.30
Purchase #7	$43.50	9.545%	$47.6521	$47.65	$47.65	$47.70
7 purchase totals =	$956.11		$1,042.3169	$1,042.31	$1,042.30	$1,042.40