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	$126.31	6.232%	$134.1816	$134.18	$134.20	$134.20
Purchase #2	$86.99	3.535%	$90.0651	$90.07	$90.05	$90.10
Purchase #3	$100.82	9.528%	$110.4261	$110.43	$110.45	$110.40
Purchase #4	$186.65	4.427%	$194.913	$194.91	$194.90	$194.90
Purchase #5	$148.35	7.869%	$160.0237	$160.02	$160.00	$160.00
Purchase #6	$41.56	3.403%	$42.9743	$42.97	$42.95	$43.00
Purchase #7	$105.49	6.150%	$111.9776	$111.98	$112.00	$112.00
7 purchase totals =	$796.17		$844.5614	$844.56	$844.55	$844.60