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	$233.31	7.468%	$250.7336	$250.73	$250.75	$250.70
Purchase #2	$54.28	5.711%	$57.3799	$57.38	$57.40	$57.40
Purchase #3	$165.66	11.662%	$184.9793	$184.98	$185.00	$185.00
Purchase #4	$51.94	4.724%	$54.3936	$54.39	$54.40	$54.40
Purchase #5	$58.40	11.122%	$64.8952	$64.90	$64.90	$64.90
Purchase #6	$82.39	8.512%	$89.403	$89.40	$89.40	$89.40
Purchase #7	$181.45	3.633%	$188.0421	$188.04	$188.05	$188.00
7 purchase totals =	$827.43		$889.8267	$889.82	$889.90	$889.80