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	$219.34	8.749%	$238.5301	$238.53	$238.55	$238.50
Purchase #2	$102.47	9.213%	$111.9106	$111.91	$111.90	$111.90
Purchase #3	$18.80	13.582%	$21.3534	$21.35	$21.35	$21.40
Purchase #4	$238.66	11.867%	$266.9818	$266.98	$267.00	$267.00
Purchase #5	$91.26	5.393%	$96.1817	$96.18	$96.20	$96.20
Purchase #6	$181.38	4.366%	$189.2991	$189.30	$189.30	$189.30
Purchase #7	$74.34	6.742%	$79.352	$79.35	$79.35	$79.40
7 purchase totals =	$926.25		$1,003.6087	$1,003.60	$1,003.65	$1,003.70