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	$69.28	13.660%	$78.7436	$78.74	$78.75	$78.70
Purchase #2	$105.84	4.169%	$110.2525	$110.25	$110.25	$110.30
Purchase #3	$237.76	9.811%	$261.0866	$261.09	$261.10	$261.10
Purchase #4	$182.81	4.656%	$191.3216	$191.32	$191.30	$191.30
Purchase #5	$10.82	9.586%	$11.8572	$11.86	$11.85	$11.90
Purchase #6	$52.53	8.747%	$57.1248	$57.12	$57.10	$57.10
Purchase #7	$52.62	3.611%	$54.5201	$54.52	$54.50	$54.50
7 purchase totals =	$711.66		$764.9064	$764.90	$764.85	$764.90