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	$170.76	4.338%	$178.1676	$178.17	$178.15	$178.20
Purchase #2	$5.87	4.708%	$6.1464	$6.15	$6.15	$6.10
Purchase #3	$37.72	13.706%	$42.8899	$42.89	$42.90	$42.90
Purchase #4	$99.84	5.560%	$105.3911	$105.39	$105.40	$105.40
Purchase #5	$229.40	12.687%	$258.504	$258.50	$258.50	$258.50
Purchase #6	$94.30	10.190%	$103.9092	$103.91	$103.90	$103.90
Purchase #7	$122.34	7.852%	$131.9461	$131.95	$131.95	$131.90
7 purchase totals =	$760.23		$826.9543	$826.96	$826.95	$826.90