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	$231.51	12.374%	$260.157	$260.16	$260.15	$260.20
Purchase #2	$50.62	3.774%	$52.5304	$52.53	$52.55	$52.50
Purchase #3	$104.56	9.836%	$114.8445	$114.84	$114.85	$114.80
Purchase #4	$72.67	9.228%	$79.376	$79.38	$79.40	$79.40
Purchase #5	$134.76	4.136%	$140.3337	$140.33	$140.35	$140.30
Purchase #6	$192.83	10.729%	$213.5187	$213.52	$213.50	$213.50
Purchase #7	$74.54	5.278%	$78.4742	$78.47	$78.45	$78.50
7 purchase totals =	$861.49		$939.2345	$939.23	$939.25	$939.20