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	$208.42	12.695%	$234.8789	$234.88	$234.90	$234.90
Purchase #2	$191.77	4.444%	$200.2923	$200.29	$200.30	$200.30
Purchase #3	$67.37	9.135%	$73.5242	$73.52	$73.50	$73.50
Purchase #4	$212.96	13.129%	$240.9195	$240.92	$240.90	$240.90
Purchase #5	$117.59	3.128%	$121.2682	$121.27	$121.25	$121.30
Purchase #6	$239.88	13.201%	$271.5466	$271.55	$271.55	$271.50
Purchase #7	$7.53	4.564%	$7.8737	$7.87	$7.85	$7.90
7 purchase totals =	$1,045.52		$1,150.3034	$1,150.30	$1,150.25	$1,150.30