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	$83.43	7.721%	$89.8716	$89.87	$89.85	$89.90
Purchase #2	$160.55	12.260%	$180.2334	$180.23	$180.25	$180.20
Purchase #3	$152.78	3.441%	$158.0372	$158.04	$158.05	$158.00
Purchase #4	$143.92	11.393%	$160.3168	$160.32	$160.30	$160.30
Purchase #5	$77.52	5.860%	$82.0627	$82.06	$82.05	$82.10
Purchase #6	$145.82	4.497%	$152.3775	$152.38	$152.40	$152.40
Purchase #7	$78.39	4.479%	$81.9011	$81.90	$81.90	$81.90
7 purchase totals =	$842.41		$904.8003	$904.80	$904.80	$904.80