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	$89.63	13.811%	$102.0088	$102.01	$102.00	$102.00
Purchase #2	$92.96	10.380%	$102.6092	$102.61	$102.60	$102.60
Purchase #3	$128.54	7.619%	$138.3335	$138.33	$138.35	$138.30
Purchase #4	$127.80	13.689%	$145.2945	$145.29	$145.30	$145.30
Purchase #5	$112.70	6.200%	$119.6874	$119.69	$119.70	$119.70
Purchase #6	$55.78	6.643%	$59.4855	$59.49	$59.50	$59.50
Purchase #7	$234.49	6.577%	$249.9124	$249.91	$249.90	$249.90
7 purchase totals =	$841.90		$917.3313	$917.33	$917.35	$917.30