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	$51.71	9.229%	$56.4823	$56.48	$56.50	$56.50
Purchase #2	$213.54	11.846%	$238.8359	$238.84	$238.85	$238.80
Purchase #3	$181.52	9.629%	$198.9986	$199.00	$199.00	$199.00
Purchase #4	$121.61	7.543%	$130.783	$130.78	$130.80	$130.80
Purchase #5	$62.85	9.386%	$68.7491	$68.75	$68.75	$68.70
Purchase #6	$196.60	4.304%	$205.0617	$205.06	$205.05	$205.10
Purchase #7	$136.37	10.662%	$150.9098	$150.91	$150.90	$150.90
7 purchase totals =	$964.20		$1,049.8204	$1,049.82	$1,049.85	$1,049.80