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	$161.40	4.388%	$168.4822	$168.48	$168.50	$168.50
Purchase #2	$181.44	3.631%	$188.0281	$188.03	$188.05	$188.00
Purchase #3	$122.38	6.502%	$130.3371	$130.34	$130.35	$130.30
Purchase #4	$17.45	5.799%	$18.4619	$18.46	$18.45	$18.50
Purchase #5	$149.98	8.225%	$162.3159	$162.32	$162.30	$162.30
Purchase #6	$176.59	5.257%	$185.8733	$185.87	$185.85	$185.90
Purchase #7	$108.45	4.238%	$113.0461	$113.05	$113.05	$113.00
7 purchase totals =	$917.69		$966.5446	$966.55	$966.55	$966.50