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	$99.30	7.647%	$106.8935	$106.89	$106.90	$106.90
Purchase #2	$98.90	6.201%	$105.0328	$105.03	$105.05	$105.00
Purchase #3	$46.73	13.612%	$53.0909	$53.09	$53.10	$53.10
Purchase #4	$144.63	9.484%	$158.3467	$158.35	$158.35	$158.30
Purchase #5	$159.96	4.119%	$166.5488	$166.55	$166.55	$166.50
Purchase #6	$83.73	13.748%	$95.2412	$95.24	$95.25	$95.20
Purchase #7	$171.41	13.688%	$194.8726	$194.87	$194.85	$194.90
7 purchase totals =	$804.66		$880.0265	$880.02	$880.05	$879.90