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	$241.97	10.293%	$266.876	$266.88	$266.90	$266.90
Purchase #2	$207.83	5.780%	$219.8426	$219.84	$219.85	$219.80
Purchase #3	$105.47	3.832%	$109.5116	$109.51	$109.50	$109.50
Purchase #4	$250.33	4.816%	$262.3859	$262.39	$262.40	$262.40
Purchase #5	$73.65	9.219%	$80.4398	$80.44	$80.45	$80.40
Purchase #6	$171.99	7.552%	$184.9787	$184.98	$185.00	$185.00
Purchase #7	$59.76	12.593%	$67.2856	$67.29	$67.30	$67.30
7 purchase totals =	$1,111.00		$1,191.3202	$1,191.33	$1,191.40	$1,191.30