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	$174.52	6.179%	$185.3036	$185.30	$185.30	$185.30
Purchase #2	$42.79	10.455%	$47.2637	$47.26	$47.25	$47.30
Purchase #3	$54.90	11.761%	$61.3568	$61.36	$61.35	$61.40
Purchase #4	$145.89	8.690%	$158.5678	$158.57	$158.55	$158.60
Purchase #5	$152.99	4.874%	$160.4467	$160.45	$160.45	$160.40
Purchase #6	$147.96	6.818%	$158.0479	$158.05	$158.05	$158.00
Purchase #7	$112.58	6.509%	$119.9078	$119.91	$119.90	$119.90
7 purchase totals =	$831.63		$890.8943	$890.90	$890.85	$890.90