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	$36.61	3.318%	$37.8247	$37.82	$37.80	$37.80
Purchase #2	$100.57	12.653%	$113.2951	$113.30	$113.30	$113.30
Purchase #3	$202.98	7.448%	$218.098	$218.10	$218.10	$218.10
Purchase #4	$71.85	10.626%	$79.4848	$79.48	$79.50	$79.50
Purchase #5	$5.28	3.230%	$5.4505	$5.45	$5.45	$5.50
Purchase #6	$115.98	6.805%	$123.8724	$123.87	$123.85	$123.90
Purchase #7	$171.98	8.636%	$186.8322	$186.83	$186.85	$186.80
7 purchase totals =	$705.25		$764.8577	$764.85	$764.85	$764.90