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	$97.55	7.252%	$104.6243	$104.62	$104.60	$104.60
Purchase #2	$227.50	9.811%	$249.82	$249.82	$249.80	$249.80
Purchase #3	$40.52	11.741%	$45.2775	$45.28	$45.30	$45.30
Purchase #4	$41.73	9.127%	$45.5387	$45.54	$45.55	$45.50
Purchase #5	$209.88	9.526%	$229.8732	$229.87	$229.85	$229.90
Purchase #6	$210.40	13.846%	$239.532	$239.53	$239.55	$239.50
Purchase #7	$151.59	4.592%	$158.551	$158.55	$158.55	$158.60
7 purchase totals =	$979.17		$1,073.2167	$1,073.21	$1,073.20	$1,073.20