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	$47.87	7.442%	$51.4325	$51.43	$51.45	$51.40
Purchase #2	$226.83	6.410%	$241.3698	$241.37	$241.35	$241.40
Purchase #3	$108.87	13.417%	$123.4771	$123.48	$123.50	$123.50
Purchase #4	$35.28	7.628%	$37.9712	$37.97	$37.95	$38.00
Purchase #5	$155.85	6.203%	$165.5174	$165.52	$165.50	$165.50
Purchase #6	$167.77	12.544%	$188.8151	$188.82	$188.80	$188.80
Purchase #7	$32.33	13.553%	$36.7117	$36.71	$36.70	$36.70
7 purchase totals =	$774.80		$845.2948	$845.30	$845.25	$845.30