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	$33.92	12.314%	$38.0969	$38.10	$38.10	$38.10
Purchase #2	$242.98	11.498%	$270.9178	$270.92	$270.90	$270.90
Purchase #3	$41.55	6.131%	$44.0974	$44.10	$44.10	$44.10
Purchase #4	$51.27	13.354%	$58.1166	$58.12	$58.10	$58.10
Purchase #5	$125.68	5.150%	$132.1525	$132.15	$132.15	$132.20
Purchase #6	$31.47	8.463%	$34.1333	$34.13	$34.15	$34.10
Purchase #7	$82.27	9.299%	$89.9203	$89.92	$89.90	$89.90
7 purchase totals =	$609.14		$667.4348	$667.44	$667.40	$667.40