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	$238.33	13.496%	$270.495	$270.50	$270.50	$270.50
Purchase #2	$40.68	5.614%	$42.9638	$42.96	$42.95	$43.00
Purchase #3	$82.33	10.620%	$91.0734	$91.07	$91.05	$91.10
Purchase #4	$229.60	10.108%	$252.808	$252.81	$252.80	$252.80
Purchase #5	$180.48	5.575%	$190.5418	$190.54	$190.55	$190.50
Purchase #6	$73.90	10.350%	$81.5487	$81.55	$81.55	$81.50
Purchase #7	$82.64	8.270%	$89.4743	$89.47	$89.45	$89.50
7 purchase totals =	$927.96		$1,018.9050	$1,018.90	$1,018.85	$1,018.90