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	$99.51	11.552%	$111.0054	$111.01	$111.00	$111.00
Purchase #2	$18.41	9.469%	$20.1532	$20.15	$20.15	$20.20
Purchase #3	$78.42	5.629%	$82.8343	$82.83	$82.85	$82.80
Purchase #4	$31.87	3.293%	$32.9195	$32.92	$32.90	$32.90
Purchase #5	$212.76	12.248%	$238.8188	$238.82	$238.80	$238.80
Purchase #6	$187.56	7.371%	$201.385	$201.39	$201.40	$201.40
Purchase #7	$225.55	11.295%	$251.0259	$251.03	$251.05	$251.00
7 purchase totals =	$854.08		$938.1421	$938.15	$938.15	$938.10