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	$45.90	12.781%	$51.7665	$51.77	$51.75	$51.80
Purchase #2	$132.95	12.505%	$149.5754	$149.58	$149.60	$149.60
Purchase #3	$127.61	12.861%	$144.0219	$144.02	$144.00	$144.00
Purchase #4	$75.61	9.613%	$82.8784	$82.88	$82.90	$82.90
Purchase #5	$32.61	7.846%	$35.1686	$35.17	$35.15	$35.20
Purchase #6	$231.31	10.483%	$255.5582	$255.56	$255.55	$255.60
Purchase #7	$30.57	11.641%	$34.1287	$34.13	$34.15	$34.10
7 purchase totals =	$676.56		$753.0977	$753.11	$753.10	$753.20