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	$124.52	12.231%	$139.75	$139.75	$139.75	$139.80
Purchase #2	$222.93	11.145%	$247.7755	$247.78	$247.80	$247.80
Purchase #3	$221.81	9.857%	$243.6738	$243.67	$243.65	$243.70
Purchase #4	$91.78	5.279%	$96.6251	$96.63	$96.65	$96.60
Purchase #5	$54.40	9.522%	$59.58	$59.58	$59.60	$59.60
Purchase #6	$223.92	7.865%	$241.5313	$241.53	$241.55	$241.50
Purchase #7	$79.64	12.778%	$89.8164	$89.82	$89.80	$89.80
7 purchase totals =	$1,019.00		$1,118.7521	$1,118.76	$1,118.80	$1,118.80