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	$42.87	6.434%	$45.6283	$45.63	$45.65	$45.60
Purchase #2	$131.44	12.235%	$147.5217	$147.52	$147.50	$147.50
Purchase #3	$31.40	6.639%	$33.4846	$33.48	$33.50	$33.50
Purchase #4	$50.94	6.425%	$54.2129	$54.21	$54.20	$54.20
Purchase #5	$42.28	7.276%	$45.3563	$45.36	$45.35	$45.40
Purchase #6	$232.32	3.234%	$239.8332	$239.83	$239.85	$239.80
Purchase #7	$86.37	13.487%	$98.0187	$98.02	$98.00	$98.00
7 purchase totals =	$617.62		$664.0557	$664.05	$664.05	$664.00