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	$40.85	10.473%	$45.1282	$45.13	$45.15	$45.10
Purchase #2	$167.43	10.398%	$184.8394	$184.84	$184.85	$184.80
Purchase #3	$92.46	12.218%	$103.7568	$103.76	$103.75	$103.80
Purchase #4	$47.90	11.747%	$53.5268	$53.53	$53.55	$53.50
Purchase #5	$192.48	11.756%	$215.1079	$215.11	$215.10	$215.10
Purchase #6	$188.27	12.109%	$211.0676	$211.07	$211.05	$211.10
Purchase #7	$24.71	3.177%	$25.495	$25.50	$25.50	$25.50
7 purchase totals =	$754.10		$838.9217	$838.94	$838.95	$838.90