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	$250.55	5.118%	$263.3731	$263.37	$263.35	$263.40
Purchase #2	$130.92	10.439%	$144.5867	$144.59	$144.60	$144.60
Purchase #3	$7.40	8.581%	$8.035	$8.04	$8.05	$8.00
Purchase #4	$23.40	3.287%	$24.1692	$24.17	$24.15	$24.20
Purchase #5	$132.54	3.832%	$137.6189	$137.62	$137.60	$137.60
Purchase #6	$210.53	5.488%	$222.0839	$222.08	$222.10	$222.10
Purchase #7	$180.84	8.645%	$196.4736	$196.47	$196.45	$196.50
7 purchase totals =	$936.18		$996.3404	$996.34	$996.30	$996.40