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	$221.68	3.121%	$228.5986	$228.60	$228.60	$228.60
Purchase #2	$40.62	12.853%	$45.8409	$45.84	$45.85	$45.80
Purchase #3	$41.46	11.722%	$46.3199	$46.32	$46.30	$46.30
Purchase #4	$205.29	12.630%	$231.2181	$231.22	$231.20	$231.20
Purchase #5	$171.84	10.810%	$190.4159	$190.42	$190.40	$190.40
Purchase #6	$215.30	3.520%	$222.8786	$222.88	$222.90	$222.90
Purchase #7	$200.29	6.408%	$213.1246	$213.12	$213.10	$213.10
7 purchase totals =	$1,096.48		$1,178.3966	$1,178.40	$1,178.35	$1,178.30