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	$181.39	12.351%	$203.7935	$203.79	$203.80	$203.80
Purchase #2	$37.57	7.567%	$40.4129	$40.41	$40.40	$40.40
Purchase #3	$127.82	7.858%	$137.8641	$137.86	$137.85	$137.90
Purchase #4	$203.88	11.555%	$227.4383	$227.44	$227.45	$227.40
Purchase #5	$85.85	4.613%	$89.8103	$89.81	$89.80	$89.80
Purchase #6	$104.90	3.384%	$108.4498	$108.45	$108.45	$108.40
Purchase #7	$79.68	8.284%	$86.2807	$86.28	$86.30	$86.30
7 purchase totals =	$821.09		$894.0496	$894.04	$894.05	$894.00