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	$244.62	3.840%	$254.0134	$254.01	$254.00	$254.00
Purchase #2	$143.64	5.385%	$151.375	$151.38	$151.40	$151.40
Purchase #3	$96.41	7.119%	$103.2734	$103.27	$103.25	$103.30
Purchase #4	$47.63	7.774%	$51.3328	$51.33	$51.35	$51.30
Purchase #5	$42.30	8.221%	$45.7775	$45.78	$45.80	$45.80
Purchase #6	$169.68	9.569%	$185.9167	$185.92	$185.90	$185.90
Purchase #7	$44.36	7.826%	$47.8316	$47.83	$47.85	$47.80
7 purchase totals =	$788.64		$839.5204	$839.52	$839.55	$839.50