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	$9.73	11.609%	$10.8596	$10.86	$10.85	$10.90
Purchase #2	$215.88	6.159%	$229.176	$229.18	$229.20	$229.20
Purchase #3	$94.51	10.595%	$104.5233	$104.52	$104.50	$104.50
Purchase #4	$122.46	12.867%	$138.2169	$138.22	$138.20	$138.20
Purchase #5	$89.95	11.420%	$100.2223	$100.22	$100.20	$100.20
Purchase #6	$86.45	11.265%	$96.1886	$96.19	$96.20	$96.20
Purchase #7	$191.43	10.145%	$210.8506	$210.85	$210.85	$210.90
7 purchase totals =	$810.41		$890.0373	$890.04	$890.00	$890.10