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	$238.93	6.801%	$255.1796	$255.18	$255.20	$255.20
Purchase #2	$214.27	5.697%	$226.477	$226.48	$226.50	$226.50
Purchase #3	$72.43	9.235%	$79.1189	$79.12	$79.10	$79.10
Purchase #4	$101.50	8.775%	$110.4066	$110.41	$110.40	$110.40
Purchase #5	$173.80	9.837%	$190.8967	$190.90	$190.90	$190.90
Purchase #6	$79.85	4.788%	$83.6732	$83.67	$83.65	$83.70
Purchase #7	$53.58	11.140%	$59.5488	$59.55	$59.55	$59.50
7 purchase totals =	$934.36		$1,005.3008	$1,005.31	$1,005.30	$1,005.30