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	$45.71	12.113%	$51.2469	$51.25	$51.25	$51.20
Purchase #2	$108.88	3.346%	$112.5231	$112.52	$112.50	$112.50
Purchase #3	$69.63	3.280%	$71.9139	$71.91	$71.90	$71.90
Purchase #4	$32.56	12.521%	$36.6368	$36.64	$36.65	$36.60
Purchase #5	$118.68	3.634%	$122.9928	$122.99	$123.00	$123.00
Purchase #6	$56.40	10.802%	$62.4923	$62.49	$62.50	$62.50
Purchase #7	$73.73	11.826%	$82.4493	$82.45	$82.45	$82.40
7 purchase totals =	$505.59		$540.2551	$540.25	$540.25	$540.10