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	$108.31	10.260%	$119.4226	$119.42	$119.40	$119.40
Purchase #2	$149.59	12.492%	$168.2768	$168.28	$168.30	$168.30
Purchase #3	$162.55	10.309%	$179.3073	$179.31	$179.30	$179.30
Purchase #4	$103.70	9.815%	$113.8782	$113.88	$113.90	$113.90
Purchase #5	$80.77	5.676%	$85.3545	$85.35	$85.35	$85.40
Purchase #6	$196.49	8.292%	$212.783	$212.78	$212.80	$212.80
Purchase #7	$215.90	8.209%	$233.6232	$233.62	$233.60	$233.60
7 purchase totals =	$1,017.31		$1,112.6456	$1,112.64	$1,112.65	$1,112.70