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	$104.98	4.371%	$109.5687	$109.57	$109.55	$109.60
Purchase #2	$73.40	12.387%	$82.4921	$82.49	$82.50	$82.50
Purchase #3	$216.72	9.360%	$237.005	$237.01	$237.00	$237.00
Purchase #4	$102.29	3.471%	$105.8405	$105.84	$105.85	$105.80
Purchase #5	$105.83	9.497%	$115.8807	$115.88	$115.90	$115.90
Purchase #6	$52.79	4.208%	$55.0114	$55.01	$55.00	$55.00
Purchase #7	$193.45	6.529%	$206.0804	$206.08	$206.10	$206.10
7 purchase totals =	$849.46		$911.8788	$911.88	$911.90	$911.90