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	$180.90	10.326%	$199.5797	$199.58	$199.60	$199.60
Purchase #2	$122.98	3.416%	$127.181	$127.18	$127.20	$127.20
Purchase #3	$141.55	9.453%	$154.9307	$154.93	$154.95	$154.90
Purchase #4	$243.33	12.215%	$273.0528	$273.05	$273.05	$273.10
Purchase #5	$123.28	3.370%	$127.4345	$127.43	$127.45	$127.40
Purchase #6	$22.87	8.702%	$24.8601	$24.86	$24.85	$24.90
Purchase #7	$92.97	11.874%	$104.0093	$104.01	$104.00	$104.00
7 purchase totals =	$927.88		$1,011.0481	$1,011.04	$1,011.10	$1,011.10