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	$232.90	7.555%	$250.4956	$250.50	$250.50	$250.50
Purchase #2	$126.49	5.263%	$133.1472	$133.15	$133.15	$133.10
Purchase #3	$128.99	10.471%	$142.4965	$142.50	$142.50	$142.50
Purchase #4	$20.77	13.383%	$23.5496	$23.55	$23.55	$23.50
Purchase #5	$119.88	13.802%	$136.4258	$136.43	$136.45	$136.40
Purchase #6	$193.58	3.383%	$200.1288	$200.13	$200.15	$200.10
Purchase #7	$46.89	7.511%	$50.4119	$50.41	$50.40	$50.40
7 purchase totals =	$869.50		$936.6554	$936.67	$936.70	$936.50