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	$140.63	5.638%	$148.5587	$148.56	$148.55	$148.60
Purchase #2	$178.67	3.708%	$185.2951	$185.30	$185.30	$185.30
Purchase #3	$145.75	4.274%	$151.9794	$151.98	$152.00	$152.00
Purchase #4	$19.86	11.234%	$22.0911	$22.09	$22.10	$22.10
Purchase #5	$106.44	11.479%	$118.6582	$118.66	$118.65	$118.70
Purchase #6	$38.29	8.208%	$41.4328	$41.43	$41.45	$41.40
Purchase #7	$93.85	4.810%	$98.3642	$98.36	$98.35	$98.40
7 purchase totals =	$723.49		$766.3795	$766.38	$766.40	$766.50