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	$18.46	10.352%	$20.371	$20.37	$20.35	$20.40
Purchase #2	$108.40	9.681%	$118.8942	$118.89	$118.90	$118.90
Purchase #3	$200.55	11.102%	$222.8151	$222.82	$222.80	$222.80
Purchase #4	$11.89	13.777%	$13.5281	$13.53	$13.55	$13.50
Purchase #5	$213.96	9.656%	$234.62	$234.62	$234.60	$234.60
Purchase #6	$227.38	10.283%	$250.7615	$250.76	$250.75	$250.80
Purchase #7	$143.39	5.335%	$151.0399	$151.04	$151.05	$151.00
7 purchase totals =	$924.03		$1,012.0298	$1,012.03	$1,012.00	$1,012.00