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	$249.68	10.278%	$275.3421	$275.34	$275.35	$275.30
Purchase #2	$87.80	3.439%	$90.8194	$90.82	$90.80	$90.80
Purchase #3	$171.62	7.853%	$185.0973	$185.10	$185.10	$185.10
Purchase #4	$63.89	6.254%	$67.8857	$67.89	$67.90	$67.90
Purchase #5	$119.93	4.566%	$125.406	$125.41	$125.40	$125.40
Purchase #6	$181.91	4.671%	$190.407	$190.41	$190.40	$190.40
Purchase #7	$233.67	8.454%	$253.4245	$253.42	$253.40	$253.40
7 purchase totals =	$1,108.50		$1,188.3820	$1,188.39	$1,188.35	$1,188.30