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	$52.40	9.721%	$57.4938	$57.49	$57.50	$57.50
Purchase #2	$79.31	3.691%	$82.2373	$82.24	$82.25	$82.20
Purchase #3	$187.46	11.705%	$209.4022	$209.40	$209.40	$209.40
Purchase #4	$172.45	6.294%	$183.304	$183.30	$183.30	$183.30
Purchase #5	$245.73	7.172%	$263.3538	$263.35	$263.35	$263.40
Purchase #6	$146.29	8.684%	$158.9938	$158.99	$159.00	$159.00
Purchase #7	$142.79	5.346%	$150.4236	$150.42	$150.40	$150.40
7 purchase totals =	$1,026.43		$1,105.2085	$1,105.19	$1,105.20	$1,105.20