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	$94.98	11.670%	$106.0642	$106.06	$106.05	$106.10
Purchase #2	$198.98	5.225%	$209.3767	$209.38	$209.40	$209.40
Purchase #3	$82.58	4.724%	$86.4811	$86.48	$86.50	$86.50
Purchase #4	$235.57	6.369%	$250.5735	$250.57	$250.55	$250.60
Purchase #5	$218.68	7.735%	$235.5949	$235.59	$235.60	$235.60
Purchase #6	$27.65	12.706%	$31.1632	$31.16	$31.15	$31.20
Purchase #7	$70.88	13.527%	$80.4679	$80.47	$80.45	$80.50
7 purchase totals =	$929.32		$999.7215	$999.71	$999.70	$999.90