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	$42.82	5.296%	$45.0877	$45.09	$45.10	$45.10
Purchase #2	$77.62	7.287%	$83.2762	$83.28	$83.30	$83.30
Purchase #3	$218.73	8.838%	$238.0614	$238.06	$238.05	$238.10
Purchase #4	$57.76	12.417%	$64.9321	$64.93	$64.95	$64.90
Purchase #5	$134.27	5.625%	$141.8227	$141.82	$141.80	$141.80
Purchase #6	$70.63	13.766%	$80.3529	$80.35	$80.35	$80.40
Purchase #7	$181.63	10.582%	$200.8501	$200.85	$200.85	$200.90
7 purchase totals =	$783.46		$854.3831	$854.38	$854.40	$854.50