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	$183.80	3.586%	$190.3911	$190.39	$190.40	$190.40
Purchase #2	$167.62	9.375%	$183.3344	$183.33	$183.35	$183.30
Purchase #3	$162.38	9.765%	$178.2364	$178.24	$178.25	$178.20
Purchase #4	$38.77	3.841%	$40.2592	$40.26	$40.25	$40.30
Purchase #5	$7.90	4.698%	$8.2711	$8.27	$8.25	$8.30
Purchase #6	$119.28	3.560%	$123.5264	$123.53	$123.55	$123.50
Purchase #7	$86.65	12.468%	$97.4535	$97.45	$97.45	$97.50
7 purchase totals =	$766.40		$821.4721	$821.47	$821.50	$821.50