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	$134.82	8.303%	$146.0141	$146.01	$146.00	$146.00
Purchase #2	$197.36	12.795%	$222.6122	$222.61	$222.60	$222.60
Purchase #3	$89.32	10.589%	$98.7781	$98.78	$98.80	$98.80
Purchase #4	$125.60	13.759%	$142.8813	$142.88	$142.90	$142.90
Purchase #5	$58.30	5.505%	$61.5094	$61.51	$61.50	$61.50
Purchase #6	$73.58	13.193%	$83.2874	$83.29	$83.30	$83.30
Purchase #7	$148.50	12.652%	$167.2882	$167.29	$167.30	$167.30
7 purchase totals =	$827.48		$922.3707	$922.37	$922.40	$922.40