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	$41.77	9.872%	$45.8935	$45.89	$45.90	$45.90
Purchase #2	$164.60	10.836%	$182.4361	$182.44	$182.45	$182.40
Purchase #3	$222.72	11.306%	$247.9007	$247.90	$247.90	$247.90
Purchase #4	$36.36	6.507%	$38.7259	$38.73	$38.75	$38.70
Purchase #5	$160.46	11.395%	$178.7444	$178.74	$178.75	$178.70
Purchase #6	$94.68	9.362%	$103.5439	$103.54	$103.55	$103.50
Purchase #7	$121.49	5.243%	$127.8597	$127.86	$127.85	$127.90
7 purchase totals =	$842.08		$925.1042	$925.10	$925.15	$925.00