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	$34.30	9.489%	$37.5547	$37.55	$37.55	$37.60
Purchase #2	$210.64	13.370%	$238.8026	$238.80	$238.80	$238.80
Purchase #3	$101.50	8.276%	$109.9001	$109.90	$109.90	$109.90
Purchase #4	$234.40	4.548%	$245.0605	$245.06	$245.05	$245.10
Purchase #5	$113.50	8.839%	$123.5323	$123.53	$123.55	$123.50
Purchase #6	$170.73	8.192%	$184.7162	$184.72	$184.70	$184.70
Purchase #7	$34.27	3.645%	$35.5191	$35.52	$35.50	$35.50
7 purchase totals =	$899.34		$975.0855	$975.08	$975.05	$975.10