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	$19.80	6.462%	$21.0795	$21.08	$21.10	$21.10
Purchase #2	$31.73	3.265%	$32.766	$32.77	$32.75	$32.80
Purchase #3	$85.73	7.266%	$91.9591	$91.96	$91.95	$92.00
Purchase #4	$139.91	8.160%	$151.3267	$151.33	$151.35	$151.30
Purchase #5	$116.82	7.139%	$125.1598	$125.16	$125.15	$125.20
Purchase #6	$173.83	7.790%	$187.3714	$187.37	$187.35	$187.40
Purchase #7	$110.43	11.578%	$123.2156	$123.22	$123.20	$123.20
7 purchase totals =	$678.25		$732.8781	$732.89	$732.85	$733.00