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	$137.40	13.682%	$156.1991	$156.20	$156.20	$156.20
Purchase #2	$150.93	8.673%	$164.0202	$164.02	$164.00	$164.00
Purchase #3	$137.42	12.522%	$154.6277	$154.63	$154.65	$154.60
Purchase #4	$94.44	11.726%	$105.514	$105.51	$105.50	$105.50
Purchase #5	$207.25	9.637%	$227.2227	$227.22	$227.20	$227.20
Purchase #6	$203.92	12.807%	$230.036	$230.04	$230.05	$230.00
Purchase #7	$31.95	5.661%	$33.7587	$33.76	$33.75	$33.80
7 purchase totals =	$963.31		$1,071.3784	$1,071.38	$1,071.35	$1,071.30