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	$34.84	10.795%	$38.601	$38.60	$38.60	$38.60
Purchase #2	$79.42	12.520%	$89.3634	$89.36	$89.35	$89.40
Purchase #3	$224.39	6.557%	$239.1033	$239.10	$239.10	$239.10
Purchase #4	$137.35	10.488%	$151.7553	$151.76	$151.75	$151.80
Purchase #5	$63.50	7.243%	$68.0993	$68.10	$68.10	$68.10
Purchase #6	$183.46	3.865%	$190.5507	$190.55	$190.55	$190.60
Purchase #7	$137.48	11.215%	$152.8984	$152.90	$152.90	$152.90
7 purchase totals =	$860.44		$930.3714	$930.37	$930.35	$930.50