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	$85.55	4.539%	$89.4331	$89.43	$89.45	$89.40
Purchase #2	$97.76	7.334%	$104.9297	$104.93	$104.95	$104.90
Purchase #3	$249.35	8.749%	$271.1656	$271.17	$271.15	$271.20
Purchase #4	$13.46	4.108%	$14.0129	$14.01	$14.00	$14.00
Purchase #5	$125.88	6.116%	$133.5788	$133.58	$133.60	$133.60
Purchase #6	$196.54	11.461%	$219.0654	$219.07	$219.05	$219.10
Purchase #7	$85.61	10.522%	$94.6179	$94.62	$94.60	$94.60
7 purchase totals =	$854.15		$926.8034	$926.81	$926.80	$926.80