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	$123.69	8.179%	$133.8066	$133.81	$133.80	$133.80
Purchase #2	$98.90	9.794%	$108.5863	$108.59	$108.60	$108.60
Purchase #3	$195.83	11.351%	$218.0587	$218.06	$218.05	$218.10
Purchase #4	$133.64	9.828%	$146.7741	$146.77	$146.75	$146.80
Purchase #5	$190.57	11.436%	$212.3636	$212.36	$212.35	$212.40
Purchase #6	$78.52	13.731%	$89.3016	$89.30	$89.30	$89.30
Purchase #7	$245.62	9.692%	$269.4255	$269.43	$269.45	$269.40
7 purchase totals =	$1,066.77		$1,178.3164	$1,178.32	$1,178.30	$1,178.40