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	$170.88	3.280%	$176.4849	$176.48	$176.50	$176.50
Purchase #2	$140.25	11.671%	$156.6186	$156.62	$156.60	$156.60
Purchase #3	$30.41	10.297%	$33.5413	$33.54	$33.55	$33.50
Purchase #4	$150.72	12.611%	$169.7273	$169.73	$169.75	$169.70
Purchase #5	$40.61	4.450%	$42.4171	$42.42	$42.40	$42.40
Purchase #6	$41.66	7.705%	$44.8699	$44.87	$44.85	$44.90
Purchase #7	$103.52	12.656%	$116.6215	$116.62	$116.60	$116.60
7 purchase totals =	$678.05		$740.2806	$740.28	$740.25	$740.20