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	$127.63	13.190%	$144.4644	$144.46	$144.45	$144.50
Purchase #2	$216.57	10.132%	$238.5129	$238.51	$238.50	$238.50
Purchase #3	$31.26	5.754%	$33.0587	$33.06	$33.05	$33.10
Purchase #4	$114.65	10.814%	$127.0483	$127.05	$127.05	$127.00
Purchase #5	$242.28	7.135%	$259.5667	$259.57	$259.55	$259.60
Purchase #6	$91.27	13.380%	$103.4819	$103.48	$103.50	$103.50
Purchase #7	$231.97	7.815%	$250.0985	$250.10	$250.10	$250.10
7 purchase totals =	$1,055.63		$1,156.2314	$1,156.23	$1,156.20	$1,156.30