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	$22.94	10.436%	$25.334	$25.33	$25.35	$25.30
Purchase #2	$128.96	11.566%	$143.8755	$143.88	$143.90	$143.90
Purchase #3	$5.42	12.474%	$6.0961	$6.10	$6.10	$6.10
Purchase #4	$102.99	8.587%	$111.8338	$111.83	$111.85	$111.80
Purchase #5	$33.26	5.560%	$35.1093	$35.11	$35.10	$35.10
Purchase #6	$103.68	5.642%	$109.5296	$109.53	$109.55	$109.50
Purchase #7	$233.42	3.335%	$241.2046	$241.20	$241.20	$241.20
7 purchase totals =	$630.67		$672.9829	$672.98	$673.05	$672.90