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	$52.50	5.622%	$55.4516	$55.45	$55.45	$55.50
Purchase #2	$16.84	8.818%	$18.325	$18.33	$18.35	$18.30
Purchase #3	$213.32	13.555%	$242.2355	$242.24	$242.25	$242.20
Purchase #4	$85.62	4.636%	$89.5893	$89.59	$89.60	$89.60
Purchase #5	$72.25	4.541%	$75.5309	$75.53	$75.55	$75.50
Purchase #6	$181.48	3.813%	$188.3998	$188.40	$188.40	$188.40
Purchase #7	$139.48	13.797%	$158.7241	$158.72	$158.70	$158.70
7 purchase totals =	$761.49		$828.2562	$828.26	$828.30	$828.20