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	$186.76	12.667%	$210.4169	$210.42	$210.40	$210.40
Purchase #2	$223.85	11.814%	$250.2956	$250.30	$250.30	$250.30
Purchase #3	$61.36	7.724%	$66.0994	$66.10	$66.10	$66.10
Purchase #4	$249.76	3.336%	$258.092	$258.09	$258.10	$258.10
Purchase #5	$94.95	4.791%	$99.4991	$99.50	$99.50	$99.50
Purchase #6	$181.84	10.428%	$200.8023	$200.80	$200.80	$200.80
Purchase #7	$105.75	12.424%	$118.8884	$118.89	$118.90	$118.90
7 purchase totals =	$1,104.27		$1,204.0937	$1,204.10	$1,204.10	$1,204.10