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	$38.70	3.126%	$39.9098	$39.91	$39.90	$39.90
Purchase #2	$82.25	13.272%	$93.1662	$93.17	$93.15	$93.20
Purchase #3	$234.53	5.810%	$248.1562	$248.16	$248.15	$248.20
Purchase #4	$114.97	11.274%	$127.9317	$127.93	$127.95	$127.90
Purchase #5	$230.98	13.814%	$262.8876	$262.89	$262.90	$262.90
Purchase #6	$88.45	12.215%	$99.2542	$99.25	$99.25	$99.30
Purchase #7	$57.32	3.365%	$59.2488	$59.25	$59.25	$59.20
7 purchase totals =	$847.20		$930.5545	$930.56	$930.55	$930.60