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	$184.76	13.469%	$209.6453	$209.65	$209.65	$209.60
Purchase #2	$92.38	9.109%	$100.7949	$100.79	$100.80	$100.80
Purchase #3	$72.80	13.202%	$82.4111	$82.41	$82.40	$82.40
Purchase #4	$54.89	9.801%	$60.2698	$60.27	$60.25	$60.30
Purchase #5	$249.56	9.652%	$273.6475	$273.65	$273.65	$273.60
Purchase #6	$104.50	12.700%	$117.7715	$117.77	$117.75	$117.80
Purchase #7	$163.98	12.388%	$184.2938	$184.29	$184.30	$184.30
7 purchase totals =	$922.87		$1,028.8339	$1,028.83	$1,028.80	$1,028.80