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	$62.45	12.449%	$70.2244	$70.22	$70.20	$70.20
Purchase #2	$36.72	7.596%	$39.5093	$39.51	$39.50	$39.50
Purchase #3	$193.68	8.102%	$209.372	$209.37	$209.35	$209.40
Purchase #4	$96.27	6.157%	$102.1973	$102.20	$102.20	$102.20
Purchase #5	$133.87	6.687%	$142.8219	$142.82	$142.80	$142.80
Purchase #6	$158.97	3.255%	$164.1445	$164.14	$164.15	$164.10
Purchase #7	$111.55	10.274%	$123.0106	$123.01	$123.00	$123.00
7 purchase totals =	$793.51		$851.2800	$851.27	$851.20	$851.20