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	$105.75	3.198%	$109.1319	$109.13	$109.15	$109.10
Purchase #2	$72.71	8.284%	$78.7333	$78.73	$78.75	$78.70
Purchase #3	$80.75	6.758%	$86.2071	$86.21	$86.20	$86.20
Purchase #4	$191.65	9.664%	$210.1711	$210.17	$210.15	$210.20
Purchase #5	$118.96	3.447%	$123.0606	$123.06	$123.05	$123.10
Purchase #6	$170.92	6.228%	$181.5649	$181.56	$181.55	$181.60
Purchase #7	$48.71	11.217%	$54.1738	$54.17	$54.15	$54.20
7 purchase totals =	$789.45		$843.0427	$843.03	$843.00	$843.10