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	$160.61	3.851%	$166.7951	$166.80	$166.80	$166.80
Purchase #2	$30.62	12.661%	$34.4968	$34.50	$34.50	$34.50
Purchase #3	$94.26	9.284%	$103.0111	$103.01	$103.00	$103.00
Purchase #4	$116.62	6.711%	$124.4464	$124.45	$124.45	$124.40
Purchase #5	$191.86	4.420%	$200.3402	$200.34	$200.35	$200.30
Purchase #6	$23.73	3.366%	$24.5288	$24.53	$24.55	$24.50
Purchase #7	$82.28	8.567%	$89.3289	$89.33	$89.35	$89.30
7 purchase totals =	$699.98		$742.9473	$742.96	$743.00	$742.80