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	$165.34	13.825%	$188.1983	$188.20	$188.20	$188.20
Purchase #2	$62.84	13.859%	$71.549	$71.55	$71.55	$71.50
Purchase #3	$59.58	10.800%	$66.0146	$66.01	$66.00	$66.00
Purchase #4	$125.95	11.806%	$140.8197	$140.82	$140.80	$140.80
Purchase #5	$226.77	6.278%	$241.0066	$241.01	$241.00	$241.00
Purchase #6	$131.59	4.764%	$137.8589	$137.86	$137.85	$137.90
Purchase #7	$43.67	3.572%	$45.2299	$45.23	$45.25	$45.20
7 purchase totals =	$815.74		$890.6770	$890.68	$890.65	$890.60