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	$79.40	12.428%	$89.2678	$89.27	$89.25	$89.30
Purchase #2	$223.99	3.308%	$231.3996	$231.40	$231.40	$231.40
Purchase #3	$191.25	6.382%	$203.4556	$203.46	$203.45	$203.50
Purchase #4	$166.56	3.184%	$171.8633	$171.86	$171.85	$171.90
Purchase #5	$100.41	5.437%	$105.8693	$105.87	$105.85	$105.90
Purchase #6	$64.41	9.501%	$70.5296	$70.53	$70.55	$70.50
Purchase #7	$185.52	4.517%	$193.8999	$193.90	$193.90	$193.90
7 purchase totals =	$1,011.54		$1,066.2851	$1,066.29	$1,066.25	$1,066.40