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	$39.88	6.418%	$42.4395	$42.44	$42.45	$42.40
Purchase #2	$90.36	13.340%	$102.414	$102.41	$102.40	$102.40
Purchase #3	$221.61	12.275%	$248.8126	$248.81	$248.80	$248.80
Purchase #4	$248.38	11.127%	$276.0172	$276.02	$276.00	$276.00
Purchase #5	$186.93	9.690%	$205.0435	$205.04	$205.05	$205.00
Purchase #6	$198.35	7.146%	$212.5241	$212.52	$212.50	$212.50
Purchase #7	$182.75	9.612%	$200.3159	$200.32	$200.30	$200.30
7 purchase totals =	$1,168.26		$1,287.5668	$1,287.56	$1,287.50	$1,287.40