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	$39.28	11.703%	$43.8769	$43.88	$43.90	$43.90
Purchase #2	$204.93	9.415%	$224.2242	$224.22	$224.20	$224.20
Purchase #3	$186.76	12.339%	$209.8043	$209.80	$209.80	$209.80
Purchase #4	$67.94	5.349%	$71.5741	$71.57	$71.55	$71.60
Purchase #5	$196.48	11.861%	$219.7845	$219.78	$219.80	$219.80
Purchase #6	$72.56	6.180%	$77.0442	$77.04	$77.05	$77.00
Purchase #7	$229.27	8.862%	$249.5879	$249.59	$249.60	$249.60
7 purchase totals =	$997.22		$1,095.8961	$1,095.88	$1,095.90	$1,095.90