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	$97.81	10.587%	$108.1651	$108.17	$108.15	$108.20
Purchase #2	$162.43	12.698%	$183.0554	$183.06	$183.05	$183.10
Purchase #3	$67.84	7.641%	$73.0237	$73.02	$73.00	$73.00
Purchase #4	$127.49	11.600%	$142.2788	$142.28	$142.30	$142.30
Purchase #5	$105.53	12.747%	$118.9819	$118.98	$119.00	$119.00
Purchase #6	$72.31	9.847%	$79.4304	$79.43	$79.45	$79.40
Purchase #7	$245.64	11.498%	$273.8837	$273.88	$273.90	$273.90
7 purchase totals =	$879.05		$978.8190	$978.82	$978.85	$978.90