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	$72.99	13.438%	$82.7984	$82.80	$82.80	$82.80
Purchase #2	$228.68	11.764%	$255.5819	$255.58	$255.60	$255.60
Purchase #3	$105.75	7.764%	$113.9604	$113.96	$113.95	$114.00
Purchase #4	$58.77	5.154%	$61.799	$61.80	$61.80	$61.80
Purchase #5	$233.64	4.295%	$243.6748	$243.67	$243.65	$243.70
Purchase #6	$149.27	12.865%	$168.4736	$168.47	$168.45	$168.50
Purchase #7	$68.91	11.416%	$76.7768	$76.78	$76.80	$76.80
7 purchase totals =	$918.01		$1,003.0649	$1,003.06	$1,003.05	$1,003.20