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	$32.59	8.526%	$35.3686	$35.37	$35.35	$35.40
Purchase #2	$43.33	3.263%	$44.7439	$44.74	$44.75	$44.70
Purchase #3	$179.48	3.184%	$185.1946	$185.19	$185.20	$185.20
Purchase #4	$103.84	7.741%	$111.8783	$111.88	$111.90	$111.90
Purchase #5	$239.90	8.190%	$259.5478	$259.55	$259.55	$259.50
Purchase #6	$96.70	12.411%	$108.7014	$108.70	$108.70	$108.70
Purchase #7	$37.58	4.616%	$39.3147	$39.31	$39.30	$39.30
7 purchase totals =	$733.42		$784.7493	$784.74	$784.75	$784.70