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	$212.27	13.423%	$240.763	$240.76	$240.75	$240.80
Purchase #2	$87.34	12.561%	$98.3108	$98.31	$98.30	$98.30
Purchase #3	$52.69	5.821%	$55.7571	$55.76	$55.75	$55.80
Purchase #4	$113.63	7.495%	$122.1466	$122.15	$122.15	$122.10
Purchase #5	$86.50	4.846%	$90.6918	$90.69	$90.70	$90.70
Purchase #6	$53.95	10.254%	$59.482	$59.48	$59.50	$59.50
Purchase #7	$95.30	8.182%	$103.0974	$103.10	$103.10	$103.10
7 purchase totals =	$701.68		$770.2487	$770.25	$770.25	$770.30