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	$15.91	13.820%	$18.1088	$18.11	$18.10	$18.10
Purchase #2	$210.35	12.747%	$237.1633	$237.16	$237.15	$237.20
Purchase #3	$110.78	4.825%	$116.1251	$116.13	$116.15	$116.10
Purchase #4	$90.69	3.626%	$93.9784	$93.98	$94.00	$94.00
Purchase #5	$52.94	12.269%	$59.4352	$59.44	$59.45	$59.40
Purchase #6	$90.73	8.355%	$98.3105	$98.31	$98.30	$98.30
Purchase #7	$112.29	9.704%	$123.1866	$123.19	$123.20	$123.20
7 purchase totals =	$683.69		$746.3079	$746.32	$746.35	$746.30