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	$89.72	11.778%	$100.2872	$100.29	$100.30	$100.30
Purchase #2	$72.85	11.780%	$81.4317	$81.43	$81.45	$81.40
Purchase #3	$63.58	5.292%	$66.9447	$66.94	$66.95	$66.90
Purchase #4	$90.82	12.734%	$102.385	$102.39	$102.40	$102.40
Purchase #5	$233.97	4.240%	$243.8903	$243.89	$243.90	$243.90
Purchase #6	$199.64	12.820%	$225.2338	$225.23	$225.25	$225.20
Purchase #7	$88.69	10.781%	$98.2517	$98.25	$98.25	$98.30
7 purchase totals =	$839.27		$918.4244	$918.42	$918.50	$918.40